FORMAL COMPLAINT: Ring Device - Ownership Transfer

I recently purchased a property that has a Ring Doorbell Pro installed. The previous owner changed the email address on his account to mine when we took ownership of the property. The previous owner then sent me the password for the account. I have logged on to the app with the information provided by the previous owner but there are no devices listed. When I try to "add device", it tells me that the device is registered to someone else. The previous owner no longer has access to the account associated with the bell to deregister the device but, as it is not showing on my account (which is the previous owner's old account) either, we now have a door bell which no-one can access, we cannot transfer, we cannot deregister, and we cannot reregister. Both the previous owner and myself have spent considerable time speaking to the call centre, the chat help, and Twitter help (last message sent 24/08 @ 10.02pm BST in case you want to track that chat) without any success. I keep being told that the previous owner has to call into Customer Services but, when he has done so, they have not been able to deregister the device from him. The previous owner is happy to receive an email from Ring asking him to relinquish the device and provide authorisation to do so but Ring will not even entertain this as an option - even though they would be able to verify the address I give them from the account records I assume. We are going around and around in circles here with no resolution and spending a considerable amount of time in trying to resolve this. When I spoke to Customer Services this morning, their "option" was to offer me a 30% discount on a new device but we just want this one working. Even more frustratingly, when I asked for an email address to make a formal complaint, I was given one which appears to be no longer working leaving me with no other options for resolving this issue.