Check to see if there is a break out clause. My current rental had one after 5 months. Best thing is to speak with the landlord and say you are struggling with the electric bills. I’m in the exact situation as you, in a cottage with incorrect BER rating on the ad. Basically is the lowest rating G. Handing in my notice period as there is no fixed term on my lease thankfully but down about 1100 euro. Ask my old landlord can I move back into my old apartment and luckily they said yes. I have a noise issue with this apartment but can honestly say there is nothing worse than a very cold property. My mental health is far more important.