What is an MP's responsibility in regards to a constituent in the community?

We have a Tory MP for my area and he's been completely useless in helping me with an HMO situation that his government and the local council forced upon me. People keep saying if you have a problem you should contact your MP, but they, (well mine) don't seem to do or want to do anything at all. I'm beginning to wonder if they only take any action when there are a vast amount of people complaining about a situation at one time - say signing a petition or loads of letters. I wonder what we have them for! If ever I end up in another situation and I'm told to contact my MP, I will just say; WHO?