If you didn't pay any money into your Cash ISA in the last tax year, you might need to reactivate your account.
To do this, you'll need to fill out a reactivation form before the tax year ends. If you don't reactivate your account, money you pay in might be returned to you.

how to close it
when using link to reactivate ISA it presumes you have already downloaded the form
Need another link to actully download form