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.
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!