Let me know if you make any progress on getting a refund.
I emailed adtbill@adt.com yesterday. I have yet to receive any response via email.
I called ADT today to ask for a refund but I was left frustrated. A very upset rep in the cancellations department insisted I do not have an account and my Canopy account number starting with CPY is not valid.
I tried to explain this is a Canopy system and how I am an active customer, but she insisted “I have been doing this a long time” and needed to be transferred somewhere else. She transferred me to “the correct department” which meant putting me over to Samsung SmartThings support 
Back when my ADT service worked I enjoyed it, but it’s really hard to get someone who can help with billing! The tech support rep I talked to yesterday from ADT said “we won’t be jerks about [a refund]” and said I’ll get a refund if I email them, but he gave me the broken billing@adtcanopy.com address.
Good luck everyone.