My phone has been ********ly blacklisted

Opened a new cell phone contract with Telkom. Used the new Telkom sim card in my old iphone (Cell C contract that was paid off) before putting it in the new iPhone (Telkom contract).

When I go to try and trade the phone in at iStore, they tell me it is blacklisted. I assumed it was Cell C given that they were the old providers.

I was wrong. I don't know what business Telkom had to blacklist my phone which was never theirs without my permission or even informing me. This cell phone was from my old Cell C contract, which was fully paid off.

Now a might battle to get this reversed . I need this phone to be removed from your black list asap.

A very poor start to a brand new contract