Is the model D7 or C7? Did you try reset it to factory settings? If no, you can have a try. Also what's the hardware and firmware version of your router? You can go to TP-LINK website to check if...

Hi, Your router is CA version, cannot upgrade to US version, on the CA website, you're on the latest firmware. http://www.tp-link.com/ca/download/Archer-C1200_V1.html

you can feedback to tplink support, send an email

did you find the 2.4G mac address of the extender under wireless statistics on the router? the mac address that you enter on the router probably is not the correct one.

you may reset the repeater if something is wrong with the product. if you mean the cloud registering thing, what could possibly go wrong? Did not receive activation email? Forgot cloud password? You...

the only way is to hard reset the router if you forgot the login password for most cases. now some of tplink routers have a password recovery function, http://www.tp-link.com/en/faq-1550.html