If I was you, I would have exported these csv along with the header line to mongodb. Excel and other tools have a limit to the number of rows and columns they can display. Now, this has worked for me because I eventually had to process the data and my go-to stack had mongodb. You can try that if you like, or:

You can go with pandas (python) to programmatically read the csv.

Advice: Avoid CSVs for huge amount of data.