Online system for customer service?

Question

CRM

Hello,
Please help me choose a system for running an online service with the following functionality:
1. User registration
2. Creating user requests (tasks for the administration of the service
3. Availability of internal billing
3.1. Availability of a user's own account available for replenishment
3.1.1. Ways of replenishment : robokassa, payonline, etc.
3.2 Issuing an invoice by an employee for payment by the user
3.3 Payment by the user of invoices
3.4 Possibility of making returns
4. Generation of an invoice and an act for the user after paying the invoice
Preferably simple and free.Thank you.

Answer 1

There are no such. All you asked for is a professional, enterprise-level system, often custom-made.