CedCommerce Amazon Channel

Be Careful With This app..... BIG TIME SCAM

So I was trying to use this app to expand my market and sell on amazon but they ask me to pay nice amount of money to list my products using their app. I didn't use their app at all and than i find out they are charging me monthly fees without my consent or without sending me any email or receipt. Now i found out they asking me to pay the recent amount and than they will see if they can process my refund or not. but they are not talking about my last few months refund which they charge me just to download their app.
Now I don't know if I should keep this app until this resolved and get charge again or what to do because they are not replying well.