Unusable internet service

For the last 2-3 weeks I have had on and off internet access in somerset region. And when it is on the performance is so bad. I pay for a 50mbps fibre and I get less than 10mbps when it is actually working. I have been complaining for weeks now and they just give the same answer over and over again (upstream fibre breakage, which is still not fixed). Now it is completely down for the last 12hours. For September I have had only a couple days of actual usable internet. I want a refund for September!!! If you cant deliver a service, I should not have to pay!