Conditional Formatting duplicating rules

[Big_Country]

When trying to use conditional formatting rules to highlight duplicate values it always highlights these same numbers which aren't duplicates. I've formatted the cells every way to prevent this but no fix yet. Shorter numbers work just fine. Attached below..PLease help 

[#2]

I'm moving this to the Excel community for better visibility.

[#3]

Some functions in Excel recognize only first 15 digits in numbers presented as text, see for example https://wmfexcel.com/2015/01/24/15-significant-digit-issue-with-sumifs-countifs-averageifs/

Same is for duplicates in conditional formatting. Alternatively you may use the rule with formula

=SUMPRODUCT(--($C2=$C$2:$C$6536))>1