Telkom is harassing me

i opened a 5Gig lte account on the 15 October 2015 and i cancelled the contract on the 19th of October 2015.<br> the reason for cancellation was that since the 15th to the day i cancelled the contract, i could still not use the device due to apparently the APN still not been activated. I am now receiving forever ending sms from telkom. Now i am receiving invoices that owe them. I have proof with me that your device was returned in god condition and i have never used any data as the service was not activated. please stop harassing me with invoices and smses. i do not owe you a cent