Amount deducted for renewal after free trial when i simultaneously canceled my subscription. No receipt on record

Hi

am hoping someone can resolve this. I had a free trial on an app that was expiring on 19th. I canceled it on 19th but around the same time i canceled i was charged for the full subscription. Now i only have my bank account statement for the transaction and the renewal amount on app store to say its for the same amount as the app i canceled. Have spoken to 4 different agents and none of them seem to understand the issue. There is no purchase receipt as well on my apple id. Pls help