I think that @pomchip might be onto something:
In countries (such as France), where the decimal point is represented by a comma, the separation character is usually a tab. So it is possible that your file is not a real csv file (comma separated values), but a tsv file (tab separated values). Which would explain the error message you are getting: your file might be called "whatever.csv", but it might not be a csv file. How did you create it?
If you open that file, you will be able to see that (and if you aren't sure, you can post a section of it here for us to double-check).
If this were the case, one way to import a tab separated file (.tsv) with base R is:
read.table("file_name.tsv", sep = "\t", header = T)
Or if you want to use the package readr from the tidyverse, then you can run:
readr::read_tsv("file_name.tsv")