Why/How would Verizon track down my new phone numbers with T-Mobile?

Had a very surreal experience yesterday.

My wife could receive phone calls on her new phone with her new T-Mobile number fine but was also receiving phone calls on the same phone from our cancelled Verizon number as well. This despite never ever mentioning to Verizon what our new numbers would be (we didn't want to or try to port over the Verizon numbers to T-Mobile)

I call T-Mobile (new company) and they say to check with Verizon. Verizon says that someone put in a call forwarding setup with our brand new numbers. Here's the thing, I anticipated some shenanigans with Verizon (for other reasons) so I have a recording of the phone call when I cancelled with them. Not only do I clearly remember but b/c I have proof I very clearly did not order a call forwarding setup.

Somehow Verizon tracked down our T-Mobile numbers and continued service with a call forwarding setup. Of course I have this second conversation recorded as well and the rep went from "You must have ordered this" to "I can't see in the system when it was setup" when I pressed for more details.

Has anyone else had this happen?