Sometimes it's not worth the worry. Some time back I was concerned with the company which offers the first clean free to win them over. I only ended up loosing one customer and in reality was pleased to see the back of them. As it happens they haven't been happy and have approached me to clean them again and I take delight in saying that I replaced their custom and with being busy I can't take any more on.
You may find this to be the case, so don't worry.
But yes, it's flipping annoying and ild be fuming myself. Reminds me when a group of trad lads moved into my area many yrs ago, we always spoke and got along. However at the time I lost some commercial work and so put some flyers out in the streets where I had been working about 6 yrs ( said its going back a bit). The boss came and had words with me, threatening he had five lads and there's only one of me and not to start a patch war. I explained my situation and also I had been there 6yrs against there one. But the bit he didn't like was when I told them that if he lost any custom to me, he wants to speak to his lads as I was double his prices. So if there prepared to pay more and come to me his crew must be doing something wrong.
So perhaps I may be tempted to post some professional flyers in a handful of his streets and if you get some and they are obviously paying more for you. It will teach him a profound lesson I'm sure