As you said "solicitor" I'm guessing you're not in the USA.

If you are in the USA, the law is on your side: just because they registered the mark doesn't take away your rights.

In addition, if they are doing something different from you (or perhaps you're using the domain for non-business purposes) they have no claim. You can open McDonald's garden shop (even if your name isn't McDonald) and unless you made it look like a McDonald's restaurant (trying to cause confusion) it's none of the restaurant company's business.

Best, unfortunately, is to get a lawyer. If your country has a "small claims" court you could even sue them to get back your lawyer costs, but those are likely to be small in any case.

Good luck!