How to cancel my I tunes subscription?

See Subscriptions and Purchases https://support.apple.com/en-euro/billing. If you think you may be able to get a refund, then use the request a refund link. It will take you to Request a refund for apps or content that you bought from Apple https://support.apple.com/en-euro/HT204084

See How long refunds from the App Store or other Apple services take https://support.apple.com/en-us/HT210904

You also may be able to get Apple telephone support for help in solving the problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

And here is how to contact iTunes worldwide support via text or chat using this link https://support.apple.com/choose-country-region/itunes After choosing your country, see the heading Tell us how we can help.

Here is how to See or cancel your subscriptions - Apple Support ... which should get you where you want.

Have you checked your subscriptions?

Purchases - View, change, or cancel your subscriptions.        

Purchases - Subscriptions not billed through Apple