you can either stoop to his level, or rise above it. Here is what I would probably do:

Write him a letter saying that someone (implying an unknown third party) is doing this to you, claiming that he (your competitor) is behind it, and that you find it hard to believe that someone with his integrity would do such a thing, and that you would like to meet with him at a convenient time to discuss a strategy to try to overcome the damage that this unknown third party is trying to do to you both.

Now you have graciously given him a way out of the mess that he has created for himself. If he responds negatively... do the best you can to educate people to the truth about the insurance/mobile service issue without mentioning him or his unethical practices. The general public are not fooled for long by people like that. In fact, most sensible people will avoid him like the plague.

Remember ... "The more dirt a person throws, the more ground he loses" . Whenever anyone mentions him, just say you would rather talk about something positive, and change the subject. There is nothing more frustrating to a mean-spirited person than someone who refuses to contend with him.

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