American Golf vs. Stephen Johnston - the saga continues

Lo, my trust in the perky and honest sounding chap on the end of the phone at American Golf to get me off his mailing list about 6 weeks ago was misplaced. I just received another monthly installment of the (for me) zero value, environmentally ruinous monthly mailing, again forwarded from my old address, which just made me mad. Grrr.

So this time, I wrote to them saying please remove me from the mailing list, enclosed their brochure, and then put it in an envelope (cost 35p) with a stamp (cost about the same). So, best part of a quid, and a couple of grey hairs later, I'm wondering if this is going to be effective, but rather expecting that it's not.