They have a bad acounting practice. if they come back and say you have an old bill to pay.
Dont pay that immediatley. first make sure you never paid that.
it hapened to me they kept saying that i never paid that bill and it went to collections also until i went through my Credit card transactions history 4 mnths back and pull that out of my credit card transaction and then immed they changed their voice and accepted that its already paid otherwise they kept saying they can see balance as pending and they couldnt even verify until i told them. Be Careful you have be warned.