Overcharged and email for cancellation ignored

I have been overcharged on my MTN account since it was transferred from Nashua Mobile in January 2015. With monthly complaints they never resolved the account and kept overcharging more every other month by increasing the amount. Finallly I stopped the payment of the October invoice as the overcharging already took the payment for October, November and December 2015. However MTN decided to suspend my services on 18 November 2018 and refused to restore until I paid the full outstanding amount until they decide to resolve the query. What a joke and I refused to pay until they resolved the accounts and processed the refunds and restored my services. Mr Lawrence Arthur informed my telephonically and via email that he will not be assisting me in getting my services restored and will never process the refunds either as he does not have the original contract. Furthermore he refused to cancel my contract when I informed him by email on 31 December 2015 to cancel when my contract expires on 1 Feb 2016. Now they want me to pay for Feb 2016 before they will give me my number back which I have had for 10 years. The arrogance attitude is what I cannot understand or Mr Lawrence Arthur.