I've just experienced the issue of "maximum of 5 devices reached" . I have only ever used this service from just one laptop using Chrome so not sure why it's not working. This looks like a poor design as it doesn't seem to be tracking the devices but rather browser use.
I now have to wait until December to use the app again. I've tried contacting the support desk several time but cannot get through and there isn't an option for TV Go issues.
It looks as if a moderator may be able to reset the devices as help desk have no idea. After a 60 min wait I talked to someone who had no idea and passed me to 2 line support person. After a few seconds I was cut off and no one bothered to try and call be back.