Vodacom legal will not respond to my emails!

I have contract with Vodacom, they have been debiting my account on the 25th but I called them change my date to the last of the month when I changed jobs. They stopped debiting from that month for I don’t know what reason. I called in again to inform them and they it was changed. Five months later they say I missed payments. I tried to query this with their legal department as it is having a negative impact on my Credit score. But I have been sending them emails for the past 3 months and have not received anything. I am so tired now because I opened this account to build my credit score and now it’s like it’s ruining my life. Vodacom needs to fix these missed payments reflecting on my score since it is their fault they weren’t debiting