if you started a refund there is no way to stop it.

If the customer started a dispute/chargeback with their credit card company there isn't a way to stop it, you can provide the details that Square is asking for to prove that the transaction is a legit transaction. 

here is a guide on how credit card disputes work.

https://squareup.com/help/us/en/article/3882-payment-disputes-walkthrough

login here to see if you have a dispute you need to fulfill, the faster you provide the answers the better, there is a time limit where it will just default to giving the money back.  https://squareup.com/dashboard/sales/disputes

EMV is also part of this with chargebacks https://squareup.com/emv-liability-shift