Autopage *******ly extends my expired contract

in 2013 I signed up for a tablet 2 GIG pm, @ R280 pm for 24 months. IN 2015 Feb Close to my contract expiry Altech sends me a sms informing me that im almost due for an upgrade, I then phone them to hear what when what... no answer (20 minutes on the phone) some days later they send me sms congratulations you have succesfully subscribed to 27 months!! I responded NO thanks I dont want to. I tried phoning them - no answer - i submitted emails on their website twice!! NO answer, April - 1st month after my contract expired they deducted R600 I tried contacting them through Facebook, phonecalls etc NO answer. Second month R1148, i then emailed their accounts who responded with the invoices. I sent them a letter cancelling everything!!!! No answer. 3rd month R1909!!!!! I stopped trying to contact them as i was waisting my time. I just reversed ALL their debit orders, and been doing so UNTIL they contact me. Today July they had a collections officer phone me for my arrears!!!! I wont pay, I didnt sign an extended contract, and why are they charging me out of contract rates if they are implying that I have a contract with them??