MTN LTE Contract - Cancelation

Does anyone have contact details for a manager at MTN? I have been trying to cancel an LTE contact (due to intermittent service) since December last year. That was eventually refused to I paid the cancelation fee and outstanding 'usage' in June this year. After numerous calls to 135 (Customer Care) and unanswered emails, I am told that my contract is still active. I am getting desperate. I would really appreciate it if someone could give me some advice.