Unable to sign in when opening Corel 2018

Every time I go to open my Corel program the Corel logo appears and a box comes up asking me to sign in. So I enter my email and password which all it asks for and a response comes back "this serial number is already used" ? Of course it is because it's my serial number. Anyone know what's up with this? I have tried contacting Tech Support but that was 5 days ago with no response.