Mobile phone number generator

Program for generating mobile phones
Good day, everyone.
I would like to get some help from the DevelStudio pros.
The question is: I want to make a program for generating mobile phones with a prefix of any choice. I need the program to generate and save the .txt file wherever the user wants it! What would a person be able to generate, for example, with "8" or "+7"; while choosing any prefix, and what would it generate (at the request of the user) from 0000014 and up to 0000021 that the total would be output in memo1.

Example: I want to generate all numbers from +7 with the prefix 933 and from 0000013 to 0000018 and it shows all this in memo1.

Then I click on the “Save” button and it saves everything that I generated in .txt to the selected location and name.

For example, I chose the desktop/new folder/PhoneGen.txt

Who's gonna help with this problem? I have a program that can do this, and I can provide it to you so you can understand its functionality, write it and I will send it to you in the LC!
I need the source!