Overcharged & Credit not passed

In March 2015 we renewed our cellphone contract & signed a contract for R130 pm for Blackberry Z3 phone with its mins + data etc. From March 2015 - October 2015 we paid R130 pm. From end of October 2015 till date we have been charged R229 pm, their excuse is we were not charged for a handset, second excuse we cancelled the contract in March 2015 & took a new contract in September 2015 that is why they have changed the subscription amount. Mtn requested a copy of the contract which was another drama to get a copy from store, upon receiving it it was sent to Mtn Call center in March 2016. On the 18 March 2016 no feedback was given so they escalated the issue. We are now in April & every time you call the call center they say its been processed & months are going by, you cantact the store, the sales rep says she will send a query & follow up & email you a feedback (get no email / reply), email the call center they say phone 808 or got to an MTN Store. No one is bothered to assist you but your money is nice to pay every month. <br> I WANT MY CREDIT that is DUE that is all I am asking.... The most pathetic cell phone provider you could ever get & the worst service. <br>