Why was the tax portion refunded to customer?

[dstudios1]

I have taxes set up to collect sales tax in my state. A customer from my state (using an address in this state) placed an order on a commission deposit and the sale originally captured the tax, but then it changed the tax to zero and refunded the tax to the customer’s credit card. How can I  reverse this? How can I reach customer support to make sure this doesn’t happen again? This is a costly error. 

[dstudios1]

Thank you so much for trying to help solve this problem. I actually never initiated a refund. It seems to have done this automatically during the checkout process. In the checkout notes, it shows the sale captured (total amount plus tax amount) and then the next note (with the same timestamp) says that the tax amount was changed from $22.46 to zero followed by a note that the $22.47 will be refunded to the customer. So the sale initially correctly collected sales tax and then immediately refunded it to the customer. Is there a way for the customer to change the tax they owe? I never issued a refund. It was all done automatically during the checkout process. I’m very confused. Is there also no Shopify customer service?