Hi Chococake,
I was in a similar boat, with only 20 participants. To 'justify' I discussed the difficulty of recruiting as well as what you just described, similar results in the data.
The below article is a good article to read about how to justify low interview rates.
Guest, G., Bunce, A., & Johnson, L. (2006). How Many Interviews Are Enough?: An Experiment with Data Saturation and Variability Field Methods. Methods, 18(1), 59-82.