Should I stop making these payments?

Several months ago my bi-polar son accessed my eBay account and put down payments on two plots of land. In order to maintain my good reputation, I have been trying to keep up with the payments, but it is very hard on Social Security. I'm old! I'm tired! I'm scared! Anyway, I have invested 4 payments of $125/mo on each of them but one is a six year committment at 9% interest. The other one is also $125/mo but is no interest and is for 20 months. I know I will lose what I have put in, but I think I should cut my losses and bail out now on the big one. I have, of course, changed my access and done whatever I can do to protect myself from further damage, but the way it is now I can't afford to get anything for myself anyway! Is it stupid to lose what is invested in order to prevent any further expense? I'm too embarrassed to ask anyone in my family since they will say - you should not have let him in the house!