Regulations will vary according to which country you live in, and
maybe also by state or county. Check with your county how far the
registration you have extends. For example, here in Australia Business
Registration for NSW covers several other states, but not all.
Generally speaking and contrary to popular opinion, a trade mark
registered in the US is only valid in the US and not internationally.
Generally, if you have used the name for sufficient time for it to be
recognized and established then it is a trade mark, though not a
registered trade mark. You can use the symbol TM but not R. It helps
in an argument if it is an original name (rather than a description of
what you do such as "John's Landscaping"), and if it is associated
with a logo designed for you and to which you hold the copyright.
Without knowing where you are and having access to local regulations
it is impossible to say whether the companies have a legal right to
operate as they are - but maybe adding "The original and the best!" or
something similar to your regular advertising may help.
Owning the domain name is irrelevant to the legal issue (though this
question is being looked at) but is a decided advantage to you. After
all, when someone is looking up yourname.com who are they going to
find - the guy in the next county, or the one with the funny spelling
- or you? If your web site isn't already a major part of your
marketing campaign, then step it up.
Taking your rivals to court is an expensive option since the issue is
very complicated. Maybe a researcher with knowledge of California
regulations can help you further.