Charged despite cancelling free trial!!!!

last week i subscribed to avast secureline 7 days free trial on google paly.i canceld the subscription on the same day due to technical problem.a few days a go i noticed that i have been charged 37.32 USD for a free trial!!!
i contacted avast several times but nobody resonds,please tell me how can i get a refund

https://support.avast.com/en-ww/article/Refund-request/

i cannot find any product ID.it serms that without product id you cannot claim for refund

https://support.google.com/googleplay/answer/2479637