I have also received a letter from HMRC. I am worried sick about it. It says "there is someone else linked to my address". I have lived alone since June 2015 & even before that I only had a house mate, nothing else. No children or partners at all.
We had separate bedrooms & lived separate lives, but shared the bills. He had half the bills in his name & me the other half, as a fair split.
I feel worried to death about this "investigation" & feel guilty, despite having done nothing wrong at all.
I want to say to them, come over & check & it will be obvi