OVERBILLED AND NOW MY ACCOUNT IS SUSPENDED

After receiving my monthly billing statement I noticed that I`ve been overbilled and that`s when I checked the previous statements and noticed on some of my statements that i have been overbilled.So I logged a complaint and I was told that I have R500 spending limit,meaning after consuming my allocated monthly 5gigabytes I have R500 to be added on my monthly subscribtion.So after complaining I was told that my case is resolved and closed,so I asked when will I be credited and I was told that the SPENDING LIMIT is been removed. So my problem is not about the SPENDING LIMIT but about being OVERBILLED because they knew the motive behind giving the SPENDING LIMIT on top of the allocated monthly expense without discussing it with the me as their customer so the SPENDING LIMIT shouldn`t be there in the first place unless it was discussed with me.Now I`m disconnected on the network.