Incorrect billing

We have 4 ****le contracts with a cap of R50 on all 4. I received and account of over R1 800 from Vodacom. I contacted their call centre and was informed that on 2 of the ****les the R50 cap was not activated. I requested all my phone calls that I have made to Vodacom about 3 weeks ago and have not received anything at all. I am aware of the fact that if you are on the internet and you reach the R50 it will not kick you out but you will be blocked the next time you try to connect. This has always happened. I am not prepared to pay an account because of Vodacom's negligence. Nobody is coming back to me and I am just told to pay the account. I am not the first one to complain about this as one of my friends have the same problem. Vodacom needs to sort this out!!!!!! I put a cap on for a reason!!!!!! We did not use R1 500 in one session. I have the proof of that