Tell people you're going to charge them!!
I see this has been posted a number of times so I suggest you maybe review your process. I have been charged today for a subscription that I neither want or need. I have cancelled my subscription and requested a refund through Google play if I don't get it back I'll take it further. I am furious. I see this is not a problem unique to me so perhaps you need to sort that out. I have not used your app and I certainly wouldn't recommend it. It's a con!!