Agreed upon service not delivered

I recently upgraded to a 10Mb/s internet line from a 4Mb/s line. This obviously cost way more. The entire time since then my speed has not increased. I have tried to phone them to sort the issue out but i have stopped as I spent around 1000 rand worth of airtime trying to get through to them which i spent on hold, so i stopped their debit order. They are basically trying to take to money for a service which they agreed to deliver but dont and then when you try a reasonable solution i.e. phoning them to sort out the issue they are basically ignoring you and costing you even more money. I have tried the live chat, still can't get through to anyone.Looks like i will have to find an ISP which doesn't just promise and never deliver and make you pay for it.