Contract still not cancelled

I've cancelled by contract with my ADSL service provider as well as with Telkom on the 11th of December 2017. I have not received any cooperation from Telkom regarding this request. Today I requested the cancellation a second time and the responds from Telkom was:

Delivery has failed to these recipients or groups:

********** The recipient's mailbox is full and can't accept new messages at this stage. Message therefore not delivered. Please try resending this message later. [Telkom SA SOC Limited. Registration nr : ***]

I am looking forward to your urgent reply on this matter!