If completed, a transaction using Apple Cash, it’s too late. There are no pending Apple Cash transactions usually. If you encounter one, please contact an Apple Cash specialist at Green Dot Bank.
Apple Cash is a service that’s administered by Green Dot Bank. Contact an Apple Cash Specialist at Green Dot Bank by calling (877)-233-8552 or by calling 1-800-MY-APPLE
https://applecash.greendot.com/termsconditions/
If the transaction is on a credit or debit card from your Wallet app, contact the fraud team at the respective bank. The phone number is usually printed on the back of the physical card.