Chances are that maybe the collection did sell these accounts, but at last minute bought the accounts back. You never know who really owns these accounts till you contact the original lendor. Ted Crosby is not suppose to be collecting PERIOD! However, if his counter-partner Dick Greenburg is the new owner, then he's next in line at the dunk tank.
Usually if a creditor says they'll take payment from you, even though they were not allowed too (but did because of error) they will contact the collection agency and inform them of payment (and in such cases, forward payment). The collection agency will then have to update their own systems. It'll be problem however, because the offices of "Interstate" aren't even set up. I'm imagining that they're ready to pack up and move again.
Regardless, the lendor needs to be informed of the practices that the collection agency is doing. One call will not be enough. After a few complaints, I'm sure the creditor will launch their own investigation. It makes them look just as bad.
Mistakes do happen. Not everyone needs to get threatened with arrest because they defaulted on a loan.
Regards-
Mike