If they actually take you to court, no problem. Make sure you show up. If you don't a judgement summary will be automatically entered against you. Now first things first, if you did not complete the application they don't have your signature to proceed (to deposit cash that is.) Thus, there is no contract between you and them so upon this you request the case to be dismissed. All you have to do is request for proof of the contract with your signature on it. They don't have it. So they don't have much of a case against you. In fact they don't have a case.
You need to strengthen your case. Gather all your documentation. Then write down what transpired in it's entirety. Include the call from them. Who called, when, what was said, etc. everything. You will present that to the judge. Your documentation is to include the bank activities. Mention that you did not touch the money as you did not know it was there and you had stopped the application. And you acted in good faith, because you could easily consider that these fools just decided to grant you cash.
You do not need a lawyer, it will be a small claims court. You can represent yourself. Go post your questions at debtorboards dot com. People there do this daily and will guide you along.
I suspect these fools will not sue you. I think they will proceed to attempt to take cash out of your account. Most likely they just might even take out their fees and penalties. Be careful. You might want to talk to your bank. Also explore suspending your account-that means no withdrawals.
After all is settled you should consider to 1-open a new account and only then 2- close this one.
You will need to educate yourself on your consumer rights under federal laws first, FDCPA and FCRA.Hit google on these:-
1-what to do when you are contacted by a collections agency.
2-your rights under federal laws FDCPA and FCRA
3-Validation of debt (VOD), cease and desist (C&D), CMRRR
4-Your state's Statute of Limitations (SOL) on debt.
5-post your questions at debtorboards dot com if things get thick