A bug in Microsoft Excel

Just found a nifty error in how Microsoft Excel is coded. When I enter a credit card number, 16 digit credit card number ending in 4, Excel removes the 4 (last digit) and replaces it with a 0. No matter how many times I enter it as a 4 Excel removes the 4 and replaces it with a 0. I tried reporting this coding error to Microsoft but I am not wasting hours of my day on some idiotic Live Chat with a Microsoft Support Idiot trying to convince the Idiot that the bug is in their software and not on my Mac. #MicrosoftSucks