You can hire a Shopify expert as a virtual assistant/technical support provider who can question your queries over the phone while you are developing your store. I also offer my service as a Shopify custom coding expert, bugs fixer, and virtual assistant.
Let me know if you need my help!
You can ask your customer to check her transaction history from her card and if your product/service is not so expensive than I would advise to just deliver the order to her because a review on Trustpilot and or Medium about your company stelling their customer's money can be very harmful to your store success. Also, get in touch with shopify store or an expert to check if there is anything wrong with your store.
Let me know if you need more help.