I was able to reactivate the connection after paying the subscription fee at https://buy.sigfox.com/. It is about 20 EUR/year. The restart subscription button did not exist until I signed up for a new contract.
Incase anyone else has this problem I managed to solve it. The problem was with my code. boot.py was set to launch main.py but there was a problem with main.py causing the connection to time out. The solution (which I found by accident) was to ctrl+c in the terminal window to kill main.py. It connected fine after that!
Thank you for all your help. We had provided Verizon the ICCID and IMEI 10 days ago at the time of provisioning request, but for some reason the IMEI was mixed up....and lost in translation. It was rectified over a troubleshooting ticket with Verizon.