How can I cancel AppleCare plan after returning the new AirPods Pro?

I ordered some AirPod Pros as a Christmas present and had to return them unopened as I had doubled up presents. No problem at all with the AirPods return in store - that’s all been processed - but having a real

issue cancelling the AppleCare that I purchased outright in store when I picked them up, less than 30 days ago.

does anyone have any advice? The online team are fairly unhelpful and keep trying to book me a telephone call with AppleCare technical support?

[Re-Titled by Moderator]