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Hi,

This sounds like a job you should hire a developer for.
If i where you i would ask your hosting company to set back a backup. I see you are using Plesk, so usually there is some form of automatic backups.

Then i would first disable your shop and find and fix the mallware that is stealing payment info. Then make a legal statement that there has been a data breach and payment info stolen. 

Then i would strongly advice to hire someone to update your Prestashop.