Please use the following link to cancel your subscription:
https://support.google.com/googleplay/answer/7018481?co=GENIE.Platform%3DAndroid&hl=en
If none of these steps seems to work, please send us a screenshot of the order number associated with your purchase. It will start with GPA. and will be available on your order confirmation email from Google.
This is how you can find your GPA number if you do not have your order confirmation email anymore: https://support.google.com/store/answer/6160235?hl=en-GB