Some 'friend,' huh?

I guess I could consider it a 'blast from the past,' but truth is...this is a past I'd pretty much rather forget.
Checking my email accounts the other day, I came across a 'friend request' from my ex-husband. At least I THINK it was from him. He has a very common name and there have been past 'friend requests' from people I've never met. There was no photo attached and when I clicked on his name, there was no background information on the sender.
Anyway...what to do?
Some background.
We were married for five years to.the.day. Yep, we filed for divorce on our fifth anniversary. It was a very low-key, no-muss, no-fuss divorce. We went our separate ways and that was that...until about 4 years ago when I got a phone call from a lawyer who was looking for my ex.
How and why did they find me? In the years since the divorce, I had returned to my maiden name and purchased a condo approximately 45 minutes from the home we had shared during the marriage.
In the phone call with the lawyer, I discovered that my ex owed approximately $20,000 in credit card debt and legal fees. But why call me? Apparently, my name was on the credit card account - even though the account was opened after the divorce was final!
I relayed this information to the lawyer and then told him the town where my ex's parents lived (last I heard anyway). Maybe they knew where he was because I had no contact at all in the years since the divorce.
Nice, huh?
And, yes, I ignored the 'friend' request.