Feels like mtn is robbing me!!

Some how mtn has changed my contract from 36 months to 39 months. And when i been asking them many times for over a month to sort this issue out I'm told they will look into it and get back to me. Even the sale person is getting no response from mtn head office. Mtn is just ignoring me. I feel like i been ****** by mtn. I asked mtn for a break down on my my contact is now on 39 months after i upgraded they can't answer. I been billed for the new and the old contract. And nobody is able to assist at mtn!!!!