Three broadband very slow

My three broadband has gone very slow. I am getting 1.5mb to 3.5 and even less than 1.5mb. I want to know is there anything I can do. I have six months left in my contact. It has been slow like this for a few weeks now and has gotten worse in the last week. I contacted three and was told part of the mast was down that was a week ago. They told me it was fixed and to reset the router. I reset the router and it made no difference. Is there a way to get out of the contract without having to pay the remainig months.