An important thing to note is that all other numbers you may have attempted before should be deleted from the PDA screen before redialling. Be sure to start with a clear screen.
Otherwise, the number should definitely be read as the paper would appear upside down, i.e. a 6 would become a 9, etc. -- but they are maybe tricky to decipher. Are you able to take a screenshot of the number as you see it, and either post it here, or e-mail it to me? The "PrtScn" button at top right of your keyboard captures an onscreen image, then come out of the game and paste it into your Paint program or similar, and save as a jpeg.
I don't have a save game at this point, unfortunately.