I Hope you have solved your problem. If not read on below
The same thing happened to me. I have two iPhone 5S's and it had "Cellular" in one and "Mobile" in the other in the Settings. I understand how annoying it is
I played around and found the solution for this.
Here's what you should do :-
->Scroll Down to International
->Check the Language.
- For BRITISH ENGLISH - Its "Mobile"
- For ENGLISH - Its "Cellular"
Change both your phone to any one of the above languages and it should solve your proble.
Let me know if it helps