Do you stalk your exes in social networks?

I had an ex who was stalking me in the cellphone. It was the time when there was no social media yet and the phone was not a smart phone yet. I just wonder when I changed the sim card (for a new phone number) my ex would still be chasing me although she never identified herself but I’m sure it was her. It only stopped when I screened people who I give my number to. In other words, one in my friends list have been forwarding my number to my ex. That did it. Although until now I still don’t know who that friend is.