E-commerce PHP Security Hardening. Fixed budget

I recently discovered unauthorized access to my PHP-based e-commerce site. Unknown customer and admin accounts have appeared, order data and site settings were altered, and several shoppers have complained about suspicious password resets... (Budget: ₹600 - ₹750 INR, Jobs: Data Protection, Incident Response, Internet Security, Malware Removal, Penetration Testing, PHP, Risk Management, Security Auditing, Web Security, Website Testing)