Hi Gp,
Yes, it's messed up that they borrowed and didn't pay you back as they promised. They are fla out wrong to do that and then to not apologize for the delay in paying you back? Just wrong.
I Timothy 5:8 says, "but if anyone does not provide for his own, and especially for those of his household, he has denied the faith and is worse than an unbeliever."
Now, the apostle Paul was speaking specifically about able-bodied adults who were not taking care of their elderly parents, grandparents, etc who were widowed and unable to live independently. But I think the principle here is that every member of the family needs to contribute financially as they are able, to help take care of the bills and basic living expenses.
If you are unable to live on your own, then your parents should be providing for you. But if you are able to work and help pay the bills and buy groceries, then you should help out with that. It sounds like it's a little of both, in this situation.
I guess you're wondering if the Bible is on your side or theirs, but it's more complicated than that. As implied already, God's position is that parents and children are to do all they can to live together peacefully and to treat each other honorably and respectfully.
So, yes! Of course your parents are wrong to not keep their word (and to blow you off as if they are entitled to take your money). But God's desire for you is that you keep an attitude of humility and forgiveness towards your parents.
Be patient GP, and keep asking God for the strength to ride this out. Continue to honor your parents. They should be setting the example for you, but perhaps God intends to use you to be a Godly example for them.
Matthew 5:42 a "Give to him who asks you, and do not turn away from him who wants to borrow from you."
Good luck, bro. I apologize if we've missed your point or not been helpful. Keep praying about it. God loves both you and your parents and wants you all to work out a peaceful and respectful solution.
Aloha.