Hi @alanhgill77, welcome to the forum and thanks for posting. I've moved your post to create your own thread as the previous thread is already resolved.
You should be able to cancel it via your MyBT, find BT Sport Monthly Pass and choose ‘Cancel subscription’. When you cancel, you can carry on watching BT Sport until your 30-day viewing period expires.
If that's not working for you check if you have more than one account on your BTID that you are choosing the BT Sport Monthly Pass account.