What are the possible ways to limit calls to the hotline 8 800?

Question

Helpdesk

Good afternoon.
There is a task to limit the number of callers to 8 800 and transfer the main flow of calls to +7 495 (regular city) in order to reduce telephony costs.
Provide access to 8 800 for customers with paid tech. support, +7 495 to provide customers with basic support.
Available number 8 800 from RT with trunks to landline numbers Garstelekom. From our side it is managed by Asterisk.
There are 2 main solutions.
1) White list of allowed numbers (not convenient, not suitable, because it is not supported)
2) A certain client code that is entered in the IVR menu and either redirects to the main menu or informs about the need to call +7 495, write letters and etc. and breaks the connection.
Have you encountered a similar situation, do you have any advice? Are there implementations of this type of task?
Thank you.

Answer 1

You can use Authenticate . Just paste in the greeting "Enter password or call 495"

Answer 2

Make a callback. "Now all operators are busy. In order to save your time, we will call you back to the number <the caller's number is being played> within a few minutes."
Incoming to 8-800 is most likely more expensive for you than outgoing to DEF...