Is it legal that a customer is forced to add a line?

I recently lost my iPhone which I had a payment plan with Xfinity Mobile. I went to an Xfinity store and asked a representative to transfer my number associated with my lost iPhone to an old phone that I had in hand. The representative told me that she couldn't do so because I had a payment plan with Xfinity. I said I would keep paying my monthly balance I owe for the phone even though I couldn't use it anymore. She insisted that I add another line with the old phone and then she would swap the phone numbers between the iPhone I lost and the old phone I had in hand. I was reluctant to do so because I had to pay $25 activation fee for this new line that I would not even be able to use. However, I had no choice because I wanted my number back.

Does anyone know if Xfinity Mobile is in a legal position to force me adding a line in order to maintain the payment plan? If not and this is happening to many people like me, can I initiate a class action against Xfinity Mobile regarding this issue?

Thank you.