I have 4g hub, and pay monthly £40, but I do not receive any emails from BT about the payment they did setup from my account.
I have no account with BT, and so I cannot login to check amount of data left.
If you're paying BT money for a service, you have an active account. If you pay by Direct Debit, check your bank statements for the reference, it's typically 2 letters followed by 8 numbers, that is your account number.
With that info, speak with the BT billing team, ask for help setting up your BT ID, then you can access your account, data usage and everything else.