Unhappy Client

I am a mtn customer for many years now and in february i upgraded one of my mtn numbers for a data package, but i decided that i am not happy with the particular deal and proceeded to cancel the upgrade within 5 days because it was in my right as a consumer, so on my next debit order mtn attempted to debit my account an amount exceeding my normal monthly amount so the debit order failed to go through, i then received an sms from mtn telling me that i owe them R1306 (opposed to my normal subscription of R541) so i then ask them why do they charge me such an absurd amount and they tell me that they made a mistake they didn't allocate the discounts that goes with the package i upgraded for and cancel they will fix it Reference nr:1- ********** 1507 but in the meantime i have to pay the R622. 39 that is in arears, i then make an arrangement that mtn must debit my account on the 9th of april which was the following day so on the morning of the 9th i receive a sms from mtn telling me that my service has been suspended i have to make a payment via the options they gave me, so i assume that there is again a debit order issue so i proceed to pay mtn online via fnb app the amount of R622. 39 on the evening of the 9th mtn debit order went through for R622. 39 so i have now paid R622.39x2 i then phone them but they tell me they automatically took the other one as the next debit that must go of on the 15th April meaning i will not be debited on the 15th, so on the morning of the 15th mtn debits me again 622.39 meaning i have now paid 622.39x3 i then phone them they tell me that they will refund me an amount of R300 because the other balance the system has already taken for the may debit order, i sent my banking details to them in a form of a statement highlighting the debit order as requested by a lady called "Melody Snyders"so i am now waiting for that refund from the 17 April which she Melody told me refund takes 3-5 days now if i owe mtn they threaten to cancel my services or they blacklist me and also charge me interest but now the tables are turned they owe me i cant blacklist them or charge interest i am disgusted with the services im receiving from mtn they are not clued up with their product/services stay away from mtn they have 0 customer service.