What's the deal with scope creep with no amendment?

I publish illustrative scenarios prepared by my practice. All participants and conversations are fictional. The fictional posts are not posts by real users, accounts of client experiences, or reports of actual results.
Illustrative scenario prepared by my practice.
For informational purposes only. This is not legal advice. Laws vary by jurisdiction. Consult a qualified attorney for advice specific to your situation.
Hypothetical question

Looking for advice on a legal issue. Here's what happened.

scope creep with no amendment. I've been dealing with this for about 15 weeks now and the situation isn't improving.

The contract was signed 22 months ago. I am not sure I have the original signed copy. The total amount in dispute is approximately $69,000.

What are my legal options here? Is it worth pursuing?