I am not a lawyer, this is no legal advice. You have to be careful. Depending on your country's laws you might have been running a financial service. These services usually require you to register, fulfill tons of requirements (at the least hold enough reserves) etc. Offering a financial service without registration might get you in a lot of trouble. The only course of action you have is to try to reverse the transactions to the checking accounts. This will largely depend on your provider.

Talk to a lawyer. Make sure you haven't been running a financial service.