What Avenues Do I Have if a Client Breaks the Terms of Contract Months Later?

[loprotomark]

Approximately 9 months ago, I completed a contract with a client (due to their unresponsiveness, actually) writing recurring content for their website. Per the job listing and contract I signed, the byline of each article was to be credited to my name and on-site bio. 

I noticed today that, two weeks ago, all bylines on the website have been changed to a generic site link. There was, of course, no conversation that this would happen and, technically, the contract is still active in my profile. 

One of my primary concerns is that much of that work is attached to my professional profile, and I do not add ghostwritten content to anything used to sell my services. Is there any avenue if the client remains unresponsive?