Customer overpaid. Tried all advice. Also cleared cookies. Also credit note not working. Payment from customer all ready in banking as well as back payment.

I'm here with some instruction that makes handling customer payments a breeze, @userilanamaree1.

You can leave the overpayment and apply it to your customer's next invoice or create a refund. Refer to the steps below:

1. Go to the + New button.
2. Click Receive payment.
3. Pick the customer, then the credit and the invoice.
4. Hit Save and Close.

To apply credit for a new invoice, open this article for the detailed steps: Handle a customer credit or overpayment in QuickBooks Online.

Then, if you want to give them a refund, please head to the Record a customer refund page for the detailed guide. 

Also, to get a list of all payments and invoices for each of your customers, you may pull up the Invoices and Received Payments report. Then, customise it so it will only show the info you need. 

Let me know how this goes and post again here if you need further assistance in handling your customer's overpayment. I'll be always around to help you in any way I can. Have a good one.