Don`t be scared about such company trying to sue you... this happens all the time. You haven`t infringed anything or broken any of the rules....
The first thing you need to do is, delete your information from the whois database.
Secondly, you are not infringing any copy rights... that only applies to physical items... items you can see or touch... We are talking about a public "domain name", here... that is "cyber"
Here read this from the uspto "
A. Use Applications
A mark composed of a domain name is registrable as a trademark or service mark only if it functions as a source identifier. The mark as depicted on the specimens must be presented in a manner that will be perceived by potential purchasers as indicating source and not as merely an informational indication of the domain name address used to access a web site. See In re Eilberg, 49 USPQ2d 1955 (TTAB 1998).
In Eilberg, the Trademark Trial and Appeal Board (Board) held that a term that only serves to identify the applicant’s domain name or the location on the Internet where the applicant’s web site appears, and does not separately identify applicant’s services, does not function as a service mark. The applicant’s proposed mark was WWW.EILBERG.COM , and the specimens showed that the mark was used on letterhead and business cards in the following manner:
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Web Developer / Owner / Consultant
When starting your own business the need to "know-how" is greater than money!