Vodacom charges out of bundle data rates *******ly

I have a data contract with Vodacom. In September last year I was charged a substantial amount for \out of bundle rates. When I queried this with Vodacom they explained that if I use more than my allocated data limit they will charge out of bundle rates. I then paid this amount and requested to Vodacom that they do not allow the account to go out of Bundle rates and to cut off the data once it is depleted. Vodacom has since on four different occasions continued to allow the account to go out of bundle with massive charges that I have to continuously request a credit for. In September 2015 I was again charged out of bundle rates for R3565. I am now advised despite a credit request and for in bundle rates to be charged for this usage