All at my expense!

Had an autopage contract which was taken over by Vodacom. 2 year contract, never missed an installment and paid up and settled. Now I've been harassed by debt collector and now lawyers saying my account is overdue and has been handed over. All at my expense. The collectors and lawyers require me to request Vodacom to provide me with a settlement letter. Why if it was Vodacom that handed me over. I've had to visit Vodacom shops and called the call center. The store can not provide me with a settlement letter because my account is settlement and closed.. Ironic right The call center struggles to view my account as the account is settled. How was I handed over? I called the call center again today and patiently wait for a letter they say they will be sending me.