Billing query

I have a contract with Vodacom including free minutes and data which I NEVER use in full. I have this specific contract now for almost 24 months. On invoice no: H5-C6W18 (01/02/2019) and H5-CRKGE (01/03/2019), I noticed amounts were charged for calls and data services, amounts: R129.76 and R43.50. I queried it with the call centre and was told that these charges are because I used up my free time which is impossible. I emailed my query to Customer services, reference numbers: 0031~JUWX and 0031~0REQ, on the 28th of Feb already but never received a reply. At that time, I have sent them a screen shot of my account online showing available 749.57MB and 68m59s talk time. This matter was never resolved. Now I have noticed on invoice H5-DJXMX (01/04/2019) and I have been charged once again the amount of R134.85 for calls and data services. I have checked my account again online and the amounts available are 1014.66MB and 230m9s for calls. I know for a fact that I never exceed the free amounts on my contract, and I would like Vodacom to resolve this matter for once and for all and credit my account with the total amount of R308.11 which is the total of the above-mentioned amounts.