Okay, just do what I tell you here, okay?
Forget about joining a gym or cutting back on wine .. here's your New Year's resolution: call up all of your existing landline, broadband, insurance, electricity, gas, and mobile suppliers, find out when your contract is up, then put a message into your diary to call them up and threaten to move to one of their suppliers. They will, most likely, bend over backwards to keep you.
I saved £450 this last year by threatening (politely) to cancel my house insurance.
I saved £200 today by threatening (politely) to cancel my broadband policy.
Add it to your diary now. February 1st sounds good.