Is it possible to find out how many other people are on your mast? I'd presume the techy guys could figure that out and see if a few users were hammering your link (if the techy guys are level one earning peanuts though then you're in trouble). When I was joining up they told me that they didn't care how much I was downloading but if I was affecting other users they'd prioritise other ports for the other users. I thought that was fair enough.
If they can't figure it out I'd move to another provider. I know you've got a contract with them but if you've got problems and they can't fix them it's them breaking the contract (I'm not a lawyer though so get more advice on that before you do anything). This thread would be relevant to you so.
The Ibb Contract