Before paying, check whether the specific course you want is included in the plan you are considering, and whether your public library already gives you access to a video course library. Those two checks can make a purchase unnecessary.
If you already subscribe, read the cancellation guide for your platform before you cancel. Each one follows the vendor's own help pages on what happens to progress, certificates and refunds. For problems inside a course, such as an assignment waiting on peer grading, use the fix-it guides, which follow the vendor's documented troubleshooting steps.