Telkom Mobile don't want to cancel 8ta modem

I have been trying to cancel my 8ta modem since the contract expired in February 2015. I called customer service & the lady told me I need to go to an outlet to fill in some paperwork. I went to the Vanderbijlpark outlet & completed all the paperwork. Received my new invoice but the modem was still on my contract. Called customer service again just to be told the paperwork have not been submitted & that i had to do it again. Went to the Brits outlet & completed all the paperwork again & was assured by the guy helping me that its been submitted to head office. Received my invoice & yet again the modem was still on my contract. Called the customer services AGAIN just to be told the paperwork have not been submitted AGAIN. I asked the gentleman that helped me what now? He said he will do everything on his side, asked me a lot of questions & after a while said someone will call me again. Now each month someone calls me & after 15 min on the phone trying to sell me another contract & me just asking for the cancellation of the current one, it is said to me that the contract is cancelled, yet 2 weeks later when i receive my invoice the modem is still on the contract. Telkom is useless!!!