Refunds on shopify

Hi guys

We are an app provider company and we encountered a serious issue regarding user refund. Has anyone had this issue and knowing how to deal?

One of our user downloaded our app and recharged a large amount of money in a short peirod of time, and used most of it on texting, but later he asked refunds on Shopify.

The thing is this user successfully refunded without our agreement to issue it.

We need consultant on this matter, we would like to know:

  1. Why did he got refund without our agreement?
  2. How do we prevent it from happening again?

Thanks a lot

难道shopfy还可以帮买家仅退款吗?shopfy到底是亚马逊一样的平台还是建站方面的服务商?