In Excel, when you input a number with a character length exceeding 15 digits, it automatically adds trailing zeros. To prevent this, you can take the following steps before entering your data:

1. Select the entire column where you intend to add the SIM (Use Ctrl+Shift+up or down arrow key).

2. Right-click, and you will find an option labeled "Format Cells." Choose this option.

After selecting "Format Cells," a pop-up window will appear, and you should choose the "Text" option from there.

After that you can paste the SIMs in the selected column and then proceed further.