PA does have a loophole in their laws that allows companies licensed in other states to lend to their consumers over the internet. But odds are, Interim Cash is not licensed to do business legally anywhere!
Since they most likely aren't licensed anywhere in the US, they can't do anything to "collect" on this debt. They can't have you arrested, they can't garnish your wages, and they can't sue you. The only thing they will do is harass you, your employer, and anyone else they have contact info for. It may be a good idea to tell your employer that this illegal company is trying to scare you out of money.
A lot of times with these foreign pdl companies, the best you can get is for them to leave you alone. I went through a similar situation with rt 66 (another foreign pdl), they called my place of employment 15 - 20 times a day, for about 2 months, even though each time they were told I didn't work there. Finally, my company had to file harassment charges. The receptionist told them that the next time they called, and the calls finally stopped.
You can file the complaints and send them letters. For sure don't give them anymore contact info or banking info. You also will want to revoke any wage assignments you may have signed. At least you already have the bank account they have info on closed.
I know their calls can be unnerving, at the least, you could have some fun with them. I would tell them the calls are being recorded, and that they are the one that will be arrested. Be creative, the only "tool" they have to collect is intimidation and harassment, take that away from them!