Advice on a credit collection?

I checked my fico score last week to notice it went down 150 points in a month. I found out a collection agency called Eastern Account System has a collection for me for about 1200 dollars coming from a phone my ex boyfriend bought back in February 2022. This was a bad time in my life, and I had completely forgotten about this and never really realized it wasn’t being paid on to begin with.. long story short, I can settle for about 650 dollars with the agency, but do I have any leg to stand on with the fact that it’s been almost four years (it was reported to collections in October 2025, last payment on the phone was August 2022) and I was never explicitly notified from Xfinity about the money I owed? Should I just settle? I’ve never dealt with something like this.