No response on emails or help on cancellation of app signup

I was cornered at Shoprite and signed up for a voucher app according to their explanation, promising me loads of vouchers for a set amount. After checking out the actual app, I am finding this is not something I want and no where near what was promised. I have repeatedly emailed them on the details given on the app to cancel it and get responses that say 24 hours - no reply. Went to bank to cancel, found they cant, so we phoned on the no they had, was different from on their own app. The guy on the phone didnt even know the app but would email clientelle to cancel- exactly what I did). I finally get an email back to say oh no you have to email a different email. No responce at all. Debit order still on my account besides a gibberish email full of letters but no words. I dont want your app!! I am literally going to have to close my bank account now. Fix this!!