Cannot sign up for free bt cloud

Clear all your browser's cache and temp files. If you are not sure how to do this then download CCleaner. It's free, safe and will clean up your system without damaging anything.
Once done try again.
If that fails try another browser.
if you haven't paid for the service then look elsewhere. Free cloud services are not recommended.
What sort of cloud service you choose will depend on your requirements. Try the 365 trial offered by https://www.storebigfile.com.
I find them quite good, especially wen transfering large files to someone else.

I know the feeling! Hard to know the answer. I suggest you get back to BT support