When I try to connect my MyQ opener I get an "Internal server error. Serial Number - " I recently switch from a different monitoring company & the garage opener was connected through alarm.com with them. I verified it is connected to the internet & is not connected to the MyQ app.
If you send us the MyQ Serial Number in a private message here off that device we can double check to make sure it is not still registered in an ADC account.
Some MyQ devices seem to be able to get in a state where they have some account data saved onboard still but the back end registration was deleted.
Try factory resetting your MyQ opener, then try connecting to wifi and registering it again.