I've been charged twice for the same order, CustomCat and Shopify integration

[juma27]

I recently started a Shopify store with just a few items, one of them is manufactured by CustomCat, I used the app from shopify to make the integration. To try out the process I made a self purchase of the item and went through with not problem but I noticed in my credit card balance (the one I used for the purchase) I've been charged twice one charge from CustomCat and a second charge from my Shopify store, I am also trying to reach out to CustomCat, I am not sure if the problem is in their part or is Shopify, and how to prevent that from happening again.