Vodacom Invoicing Mayhem Again

I have a data and an airtime contract with Vodacom and for the first nine months everything was good including the invoicing. Needless to say, Vodacom suddenly decided to increase my premiums without notification and I enquired in writing about this 5 months ago and still await their response! Seems with this crowd a person has to scrutinise each invoice! I tried calling them and after hanging on for a long time, they dropped my call - This obviously could happen to anyone but in my current state of mind with these guys, it was not welcome!