Wrongful Billing and Poor Customer Service

I called in on the 16th September to query my billing which was over the expected billing amount. I was then explained that there was additional usage of data which I then requested that they put a limitation to it and on all calls as well, but it seems that it was not done. This month I received a billing of over double the amount that I am supposed to pay. Today I requested for a call from an agent and I was not helped at all. The lady couldn't resolve my query and said she'd transfer me to sales dept but I got cut of. This is just unacceptable that we get treated this way. This contract phone is for my son and I was planning on getting another one with them for myself but by the look of things, I will pass.