Can a company still collect a debt when they sold the account to a debt collector?

I would suggest that you immediately retain an attorney to file a motion to set aside or refund the garnishment. If the debt is transferred or sold, they are no longer in privity (directly connected) with you and should not be the garnisher. Rather the new company should. The only exception would be that the new company is really an alter ego of the original creditor.

The debt (and the costs, expenses, interest, fees and penalties allowed by the contract or Court judgment) can only be collected once. Anything recovered must be accounted for and collected against the balance. As for the obligation of the debt being "sold off", I would have to see the evidence of that. Generally, in that case, the new owner of the debt has collection rights. No firm opinion possible without the details.

It is fishy.. they cannot sell the debt and collect it at the same time.. Now the debt collection company might not own the debt.. it might only be charged with collecting it for a fee.. Contact the new company that they sold the debt to and provide them the paperwork. Or contact an attorney that could file a lawsuit against the two companies to determine your rights (and sue the wrong one for violations of the fair debt collection act).