10mb Lie!!!

We are paying for a 10mb line, they charge us for a 10mb line and im getting a 4mb line.... technical side said the exchange can only give 4mb. now the accounts department is charging us the price for a 10mb line and when you try to get this sorted they keep transferring you between departments. My problem is we did have 10mb line speed in the past and all of a sudden its down to 4mb and they say they can't change it back. I think telkom has not been honest with me and I'm really fed up with their service which is non existent. Give me back my 10mb line and don't dare charge me to get it back to 10mb.