I'm concerned that someone hacked into my computer from an online site to steal information. Is that possible?
From what you describe, no. Adware's typical goal is to convince you to spend money on something you don't need. If you were to call that telephone number they would gleefully accept credit card payment in whatever amount they can convince you to spend, for the answer that you just got on this site for free. That assumes they know what they're doing, which isn't guaranteed.
A greater threat is that during the phone conversation, they convince you to install a remote access tool (a/k/a RAT - TeamViewer is an example of one) that would enable them to log in to your computer remotely for whatever nefarious purpose that may entail. Clearly you didn't do that.
In an abundance of caution, go to the Safari menu > Preferences > Privacy, and select Remove All Website Data... > Remove Now.
You will need to sign in again with all websites that require authentication (such as this one).