Instacart Overcharged, Drove Me Crazy About Out-of-Stock Items, Refund Denials

My recent Instacart orders are like no other in the worst sense…In my past four orders alone, I've had annoying and def dissuasive problems…If I have to be honest, Instacart has been responsive in refunding missing or damaged items, none of these items exceeded $7…I was so happy with it I would just place orders worth of $100 monthly, of course before it went ballistic. Yesterday for example, placed an order that included fresh greenery, my shopper informed me they were out of stock, I selected an alternative option and explicitly instructed them to remove the out-of-stock item from my cart. Yet now I see both charges on my card. Today, received an email from Instacart stating that they would not issue a refund for the duplicate charge. Excuse me but why? Their error resulted in an additional charge of nearly $20. No thx again.