If you don't pay back the money when it is due, the bank will send a reminder to your classmate to remind him to pay back the money. If you don't pay for nine consecutive periods, the bank will send a lawyer's letter and the house will be ready to be taken over. In case of unpaid payment during 12, the bank will have the right to submit the house for auction.
And most importantly, it will be more difficult for your classmates to borrow money (no matter what bank) in the future.
Take care! ! I hope you're just kidding.