Why charged me in trial period for “betterme” application?

i downloaded an app called ‘betterme’ and in the application information saying it will charge me after my trial period, but they charging me immediately after I Instaled the application and I received msg from my bank that I payed about this application. The money in my bank account are block now , but I don’t want to pay about this application and want to umblock my money I wanted to try it in trial period!!!!! i also canceled in subscription properly in my iPhone. The team of “better me” said that they doesn’t charging about trial period and I have to request Apple to refund my money. i Have a need of information how to back my money!