Checkers SIXTY60 is ****! BIG ****!!!

I have made several transactions with checkers sixty60 app. My goods are always delivered on time but I am always charged extra incase they have to replace unavailable items with a substitute. But everytime my order always amounts to less than the amount debited and the difference is never refunded into my account on all the occasions I have placed an order qith them. I am beginning to hate checkers sixty60 already!!!! They are ****s