I would start looking for rooms for rent in your area, and price that rent against the rent that you are paying your parents. Basically, you are renting a room from your parents anyway. Go to the properties and talk with the landlords, and see if you can find one who is a believer in Christ (for real). Talk to people at your local church and see if any of them have a room for rent, or know a Christian who does. Make sure that they will let you use their kitchen and mailbox on their property - that should come included with the room.
If the market price for a room is lower than what you are paying your parents and you can find a supportive Christian landlord, move out of there as quickly as you can. Take everything that you want to see again. They are unbelievers and will not support where God is leading you, and there will be more of these petty disputes. You don't want items that are valuable or useful to you in their hands.
2 Corinthians 6:14 said:
Do not be mismatched with unbelievers; for what do righteousness and lawlessness share together, or what does light have in common with darkness?
(This verse is commonly applied to marriage, but this frequently applies to business arrangements as well like landlord/tenant. Your obedience to this Scripture is more important than your giving to your church.)
If the market price for a room for rent is more than what you are paying your parents, reduce your church giving, and put it toward the house fund. In this case, you will need to do another set of math. Take the prices for homes in your area, and the number that you currently have in your house savings account. Do the math with that number as a down payment and calculate the mortgage payment for each options that appeal to you. Next, add up the total cost of ownership for each of those options. That would include property taxes, repair estimates, insurance, and utilities. (You may also want to take a homeowner training course, psst, they have those. Learn what you're getting yourself into.)
Next, increase your down payment until the total monthly cost of ownership of your intended house is lower than the rent you are paying your parents. If that is too high no matter what, do another calculation where you increase your down payment until the mortgage payment is less than what you are paying your parents. At that point, you might as well put that money into your house instead of losing it to Mom and Dad.
Next, calculate your total current savings rate per month, subtract your current amount of money in the bank, and, based on your current rate of saving, calculate the number of months that it will take for you to get your house money. Then give yourself at least 6 months for house hunting time, since you're employed.
Write it down as a formal statement: I am saving for a house. I am earning X income per month and I am saving Y. At my current rate of saving, it will take me Z months (or years) to earn the money for the house. I expect to move out of this house in A months/ years.
Then take it your parents and tell them. Just rip the Band-Aid off. You'll find out what their real intentions are soon enough. If they are merely interested in your success, you'll get a smile and a pat on the back for being financially responsible. Maybe you'll even get your rent money back. If there is some negative spiritual interest behind this, you just told them that you're not going to put up with it. Your relationship with God is important to you. The statement will bring the truth to the surface, and you'll know what's really behind this.
Cases:
1. If Y number is proportionately low and Z is really high (like 10 years) you probably will need to evaluate your savings rate, whether it can be increased by cutting out frivolous purchases or looking for cheaper or even free options like OfferUp or thrift stores. You may also want to evaluate your choice of house, can you find a less expensive one? Maybe the house savings idea is not a good one, and you just need to rent an apartment and get out of there. Maybe you need to look for an opportunity to increase your income.
God may want you to do what your parents do not want you to do. If you delay following God's lead, you will just suffer. Frankly, it's just painful anyway when God leads you to something that your parents don't approve of, but if it's your parents versus God, God always wins. Look for God's provision and His guidance on how He wants you to move forward. He has brought this problem into your life for a reason, and His solution to it may not be what you want.
At this point, I don't want you to be frightened, but I do want you to get more clarity on your situation and understand how bad it truly is. One of my friends got thrown out of his unbeliever parents house onto the street and his mom got him fired from his job through repeated slanderous phone calls to his workplace. He's still living out of his car. And your parents, who are unbelievers, have already expressed hostility to your Christian faith and threatened to increase your rent. I don't want you to end up in his situation. You're far better off renting and giving up the house forever than ending up like him, so evaluate how bad your situation truly is and pray for wisdom and discernment as to what to do. And while you're at it, make sure your car is paid off, you have the clear title to it, and that you don't have a loan on it before you do anything having to do with the house, because that could turn your situation into a nightmare if you get kicked out unexpectedly.
Bottom line: Get out of there. But do it intelligently.
