How can we generate 14 digit numeric number.But that number should not repeat ever?

You mean a 14 digit long random number?
Well, first of all it depend on the usage. If it is for cryptography need, than it is more complicated. Let's suppose you need it for general purpose, and let's suppose also, that you don't want to make them globally unique.

Random is random - it means that collisions can happen. The collision can be handled in two ways:
1) you generate the random number, and store it; the next time you generate a number, you check in the storage - if you have it already, you generate a new one.
2) you deal with the collision probability - is is acceptable at a level of let's say 1:2^200 ?

And there is an other question: how many instances do you want? Because you will run out of numbers after 10^14 instances.

So please clarify....

what have you done so far?