Dearest Reborn... may you have peace!
First, may I say that, yes, under the Law Covenant a debt was to be repaid. However, also under that Law, a debt was to be FORGIVEN. This issue holds true under the New Covenant, too... "forgive us OUR debts, as WE forgive others theirs..." etc., etc. Their is a thought here that you might be missing.
May I suggest, then, that you consider it a gift 'made to God'... and let HIM 'repay' you? For His arm is not 'short'... and if you apply this, then the Truth is that whatever YOU 'measured' out (and, well, yeah, you OBVIOUSLY 'measured' it, didn't you?)... will be 'measured' out to YOU... pressed down... and overflowing.
Failing THAT... and should you be in dire need... let me know and I will personally send you the fifty bucks. My Father, then, the Holy One of Israel, JAH OF ARMIES, will in turn, repay... me. I have NO doubt.
But, please... don't 'harass' these folks over such a small amount (I know, it is not small to YOU). For if you don't forgive this child his debt (yes, I know, he is '18', and so no longer a child.... er, right...), how then will you be forgiven YOUR debts? (Yes, I know... you don't have any debts... you pay them all...)
Again, I bid you peace, and I am...
YOUR servant and a slave of Christ,
SJ