Legal Question in Consumer Law in Pennsylvania

What do you mean "what are your options?" Obviously there is a problem here and before it becomes a bigger one you need to get this straightened out. Review your bank statements. Did the check clear or not? If you do not have your bank statements then you will have to go to your bank and get a copy of the check.

If the check cleared then Aaron's is mistaken. In such case, you would need to write them a letter, provide a copy of the check and a copy of the lease saying that it was paid in full and ask them to investigate. If the bank shows that the check never cleared due to insufficient funds, the responsible thing to do would be to pay the missed payment. Don't re;y on the law of mistake as I am not clear here exactly on whether Aaron's was mistaken or whether both of you could be mistaken.