A few years ago I also found a serious bug in a debt collection agencies web software. I ordered a phone and neglected to pay import tax and was chased by the agency. I found their website and saw that they developed their management software in-house and made it available for purchase for other agencies. They offered a demo which I used to navigate around, in the demo was a reporting tool which essentially allowed y…
You don't erase just your debt, you open up Tor browser and drop the entire database. That'll teach them for next time.
Apart from being a federal crime (CFAA), it would be rather obvious by the logs that a user was testing SQL injection on the demo system minutes before the production system was vandalised.
A better option would be to pay the debt, and then let them know you found a potential issue on their demo system. Let them connect the dots between demo system and production system. If they can't make the logical leap, then they deserve whatever someone else does.