Non-existent service from Vodacom accounts department!!

I upgraded my account to a SmartS+ with promotional Iphone 6 in August 2017 with a promotional monthly rate of R349.99. I then added the caller Identity subscription for R10pm which should have brought my monthly subscription fee to R360pm. However since September 2017 Vodacom has proceeded to charge me the full subscription fee of R460pm - on my invoice it shows the deduction of R87.72 (excl vat) en then they simply charge the R87.72 back again thereby never granting the discount. I have phoned customer care/accounts every month since Oct2017 and have only once been able to rectify this matter. Since Nov 2017 Vodacom seems unable to understand and correct this and are thus **********ly overcharging me every month. When speaking to any customer care/accounts consultant they are always very polite and willing but once they have established the problem I am explaining to them they say it has to be escalated and that I will receive a reference number via sms- this does not always happen and sometimes I receive a sms saying the query has been resolved without me even receiving any feedbac****!! This is incredibly frustrating!!! Staff at Vodashop are also unable to do anything as it is an Accounts issue. Can anyone please help ????