Unable to add custom domain to my existing hosting

Website URL

SQUIG.CT.WS

Error Message

Squig dot net is already assigned to an account and in use on another account..

Other Information

Trying to add my custom domain squig dot net to an infinityfree hosted site. I set my nameservers at my domain registrar but I’m getting a message that my DNS is hosted elsewhere. Looking at infinityfree DNS for my site I added the CNAME records as well, but clicking “Add Domain” gives the error that squig dot net already exists.