Instacart problems

I have had some really poor experiences with instacart. One with a Publix order and one with a Costco order. The one with Publix was an order I placed and was unable to pick up on time due to illness. I called the store and was assured the items would be restocked and a refund would be issued. Never happened. I went to customer service at my local Publix and was told the refund would appear soon and from Instacart. This was a small order and I just dismissed after not seeing any refund on my account after 2-3 months of checking it.
My next problem was with a large order I placed with Costco to be delivered. I saw my receipt from Costco in my email and on my Costco online account, looked ok. Then I saw the amount taken out of my account for that delivery, a $47 difference from what was showing on my receipt and website . I was shocked, I took my printouts of the email, website and bank account to customer service at my local Costco…no explanation. Called Instacart customer service with all my info…no explanation…Costco said it was Instacart’s problem, Instacart said it was Costcos problem. Costco corporate referred me back to Instacart. I spent two days of attempts to straighten this out and get a decent explanations to why I was charged $47 more than my receipt. I was quite aware of the service charge, tip and mark up of items over store cost but $47??? And not one person could explain the differences??? I am done with Instacart…Only in an emergency situation will I use them and I will give the tip in person to the delivery person.