You haven't said what application you have used to export the data, nor have
you said in what format the data is exported, nor by what means you have
imported the data to Excel. If you look carefully at the data, either in
Excel or in something like Notepad, you might see the problem. One of the
most frequent problems is the introduction of extraneous spaces or
non-printable characters, so I would look for those first. You'll need to
sort out what the problem is before you can cure it. If you've put the data
in as text, merely changing the cell format to number won't change the
content of the cell. A format change merely changes how it's displayed.
Sometimes you can get away with using Edit/ Paste Special to multiply by 1
or to add zero.