Need help to secure my new portal by all rules of the art in terms of security and privacy. -- 2

I am about to go live with a new online service thats core business is the hosting and distribution of NonVoip Numbers (prepaid Sim Cards hosted with Mini Sim Pirts + API) and need an affordable Cybersecurity Specialist that helps me actively to get this portal shielded in all Security and Privacy related aspects. The Portal is developed in C# .net core and some Basics like Captchas are already integrated.