"They have an office in town, I sometimes wonder what nastiness I could post through their door and stay on the right side of the law."
We used to get mailings for a former tenant from a college he attended. As he was studying for the church it should have been fairly straightforward for them to check the relevant directories for an up-to-date address. When I got fed up with returning them I rang them up and told them that in future I'd keep returning them but there would be a £10 handling charge each time and I'd go to the small claims court if it wasn't paid. They stopped.