Yesterday I got a phone call from my friend. He asked me he was trying to enter some serial numbers of SIM cards in excel cell. Those numbers were of 19 digits length. He told me, the digit of sixteenth place and onwards changed to zero. I tried the same. He was right.
To overcome the issue I changed the cells format to text rather than number. It worked. Now if you enter number containing more than 15 digits it remain same as you entered. Because the value you entered is now considered as a text.
But the only problem is that you can not make any calculations using these cells. But you have managed to enter long numbers like credit card number etc.