MTN - we make up the billing rules as we go along!!

My complaint is in regard to an overcharge on my account, as reflected on my account invoice dated August 2020, for which I have requested a refund. The issue is as follows: - I had a 24 month promotional data offer from MTN which ended recently. On speaking to an MTN consultant, it was stated that when a promotion ends, a customer will be billed for any promotional amounts until such time as the customer ends the contract. - At the end of the 24 month promotional contract I had, I was billed for the promo data for 1 month, but then not for the subsequent 2 months. - No MTN consultant can explain why I was not billed for the following 2 months, as I had made no contact with MTN to end any promotional data bundle. - I was informed that the billing clause is in the ‘contract’ – I have asked for a copy of the contract that stipulates that I must end the promotional offer. I have yet to receive this information. - On 23 October I got 3 SMS’s stating a change to my billing – I do not know why anything was changed as I never requested any changes. - The standard response that I now get from MTN is: " Please note that service fees are billed in advance therefore based on term date, customer is billed pro-rata on discounted subs and pro-rata on standard subs. All VAS services are also billed in advance, therefore will be also be billed pro-rata. No credit due. Please log to system support to have service removed if customer no longer requires the service." This response makes no sense as I have no idea what services are being referred to and why pro-rata billing is even mentioned - I have asked on numerous occasions for this to be explained and receive a stock answer that this is the reply from the billing department. - I was even told by a consultant to forget about this issue as MTN will not refund. I'm not sure how the consultant knows this, unless it is part of their training? - I have been a loyal MTN customer for more than 15 years with absolutely no issues. However, this experience is making me reconsider my options. - I have previously requested that this matter be referred to management of MTN – I again request that this be done, so as to avoid another standard response from MTN’s billing department.