Timestamp Formula Auto Deleted when Using Macro

Hi Team,

Need help on this tracker that I'm currently working on. I'm wondering that every time I'm entering new information using the macro to auto populate the person's information, my formula for Column C is auto deleted. I need to manually type in "CLOSED" in Column M and the current time should appear in Column C. My formulas are working if I type in "CLOSED" in a blank row, but when I use the macro to auto populate some information, the formula is no longer working.

Unfortunately, there's no way for me to attach the tracker with the data entry form due to it's capacity. Please bare with the attached sample sheet.

Thanks,

Emmieshane