No end to terrible line speed

I have a 2 year contract with this ISP for a 20/20 mbps line. Since the 12th of August the line has been running at 0,2 / 9,0. I have been logging queries for the past 3 days. After every call, the speed is better. An hour later, it is back to its unacceptable speed which is not what I am paying for. I am not sure Vox are able to address this. I suggest some sort of regulatory body as some ISP's do not care whether they deliver according to the contracts and come end of the month, the full installment will be deducted from my bank account.