I spend too much time watching TV, but there is this show about people who go bad on debts. The Sheriff sends along guys who come into homes to evaluate the worth of the property within and then haul it away. There was one episode with a case similar to yours - the woman didn't actually live there and hadn't for some time. The reposessors were still going to take the current resident's stuff because they had a court order to do so, until the people at that address could prove to them that their name was on the lease and not the deadbeat's. (!) Might do to keep a copy of your council tax letter and your lease agreement handy?
We've been getting mail for the former tenants of our place, who haven't lived here since early 2017. I was marking it "not at this address, return to sender." On one (which was a bank card statement) I wrote on it "has not lived here since Feb 2017, return to sender". They kept sending them, though. So after I year I just started binning it as it arrived. There was even a supposed delivery of some baby-associated item (a pram?) that we had to turn away, six months into our own tennancy. I was wondering if it was a collector trying to sort out if we were "them" by doing a "signed delivery to" scam? Then the dunning (I assume) notices started arriving. Some stuff from HMRC, that I did the "return to sender" thing on. Every now and then we STILL get stuff for them, which promptly gets binned. It's been almost two years, so, really?