Ongoing contract after auto-termination in 24mnths

I took up a cellphone contract in 2013 commencing in April, and my contract stated that it will auto cancel after 24 months. On the 18th March 2015 I got an email informing me that I'm due for an upgrade. This means that they were aware of the fact that my contract was ending in a month. I stopped using the tablet for several months now which is fine because I knew it was coming to an end soon. To my surprise there was an instalment that went off in May 2015 and the last one was supposed to be in April 2015. I am still not using the 2gig data that they load but I was under the impression that they will close it as it was a \mistake"and it's supposed to auto-terminate in 24 months as I was informed. I did not make provisioning for the debit order in June on purpose but a double instalment went off in July. I went to the bank and advised them to reverse that transaction. I have advised them about the whole situation about my contract ending in June 2015"