If you are registered for VAT it should always be activated. You cannot choose when to collect VAT or not, and your customers cannot choose if they want to pay VAT or not. Only by entering a valid VAT exemption number can they pay zero VAT.
If you are not registered for VAT, you should turn it off.
To open a new support ticket, first select the relevant forum and then click the "New Post" button. Example: You need support for the core plugin? Click on Core Plugin support and click on the "New Post" Button.