Guys, it's impossible for you to have both Fortmatic and Metmask at the same time. If you had Fortmatic and exported your Private Key, and imported it correctly into MetaMask then you will be able to login using Metmask. However, as soon as you export your key from Fortmatic then you no longer have a Fortmatic account!
What's happening is people are exporting their Fortmatic private keys, importing them (probably) incorrectly into Metamask, and when they can't login they try to login with Fortmatic - except it doesn't work and prompts a new wallet registration.
YOU CAN ONLY USE ONE WALLET AT A TIME