There is a button on the side of the Stick; hold it in for 15 seconds to reset the Stick and see if that improves things.
Download the free Ookla Speedtest to your laptop, and report back what download and upload speeds it sees.
If these are not the speeds your ISP promised you, contact them and complain.
Set a Payment PIN on your account so that no-one but you can buy memberships on it. Check your bank accounts monthly for any other unexpected payments to Now. That way you can at least nip them in the bud, while you and Now figure out whose fault they are.