fileID doesn't update when importing data using for loop

I'm using Matlab's import data code generator to pass data to a series of commands. This works fine when I run the script and reference a single file, but if I loop through several files, my variables aren't updated as I expect. I believe I have traced the problem to 'fileID' not updating after the first iteration of the loop.

In the code below, I can confirm that 'filename' is updated with each iteration of the loop, while 'fileID' is not. Consequently, the same vector is assigned to the variable 'y' in each iteration.

Can anyone suggest where I am going wrong?

FileList = dir('*.csv');
N = size(FileList,1);
for k = 1:N
 % get the file name:
   filename = FileList(k).name;

delimiter = ',';
startRow = 2;
%%Format string for each line of text:
%   column2: double (%f)
%  column3: double (%f)
%   column4: double (%f)
%  column5: double (%f)
% For more information, see the TEXTSCAN documentation.
formatSpec = '%*s%f%f%f%f%[^\n\r]';

%%Open the text file.
fileID = fopen(filename,'r');

%%Read columns of data according to format string.
 dataArray = textscan(fileID, formatSpec, 'Delimiter', delimiter, 'HeaderLines' ,startRow-1, 'ReturnOnError', false);

%%Close the text file.
fclose(fileID);

%%Allocate imported array to column variable names
O1 = dataArray{:, 1};
H1 = dataArray{:, 2};
L1 = dataArray{:, 3};
C1 = dataArray{:, 4};

%%Test filename and fileID
filename
fileID

%%Clear temporary variables
clearvars filename delimiter startRow formatSpec fileID dataArray ans;

y=C1;
figure 
plot(y);

end

[Adam]

I can't see anything wrong at a glance with that. fileID is clearly getting re-assigned though if you get the same data each time because if it weren't it would be at the end of the file next time round and read in nothing.