This doesn't solve the question but provides another solution to the need. Find length of the file and instead of trying to read the sheet name, we can read the sheet position by inputting the length into the sheet section of xlsread.
MS_xlsx=dir('*.xlsx'); % list of the files
for i=1:length(MS_xlsx)
[~,file]=xlsfinfo(MS_xlsx(i).name);
L=length(file);
[~,txt]=xlsread(MS_xlsx(i).name,L,'B2'); % read the text
if strcmp(txt,'Number:')
delete(MX_xlsx(i).name)
end
end