Poor Customer Service

We relocated to the US the end of December and knowing this, i sent through my cancellation to MTN the end of November with the understanding that a month notice needs to be supp****. I hear nothing back from MTN even after numerous phone calls and e-mails. At the end of December i got a mail from retention which asked why i was cancelling to which i explained that we were moving. Again no reply after the mail until i sent another e-mail as follow up. I got a mail back saying that they will continue with the cancellation but i had to pay for January and February. Why do i need to pay for those 2 months? I sent through the cancellation as per the agreement of a month's notice and did so knowing i was not going to be in the country anymore after December. I am getting penalized for their negligence and i refuse to pay the outstanding balance. Again i have sent mails for follow up but have not had one reply. Their customer service is bad and this is what i get for being with them for years and have always paid my account on time. This in unacceptable and now have to try an resolve this from halfway across the world