Why does cellular data usage on iPhone 6 not match phone company data?

[iMore Question]

Phone company records show 129 MB used this period - my iPhone 6 shows 1.9 Gb.
Why the difference?

 

[MrMike6by9]

Are you certain you're using the same cutoff date for your usage?

 

[Ariel Babalao]

Your iPhone probably record your data usage when on wifi as well. Thus resulting of a total usage of 1.9gb