You can try with this expression
System.Text.RegularExpressions.Regex.Match(YourString,"\b\d{8}(?=NEFT)").Tostring
This expression is based on the NEFT that appeared after the number

System.Text.RegularExpressions.Regex.Match(YourString,"\b\d{8}").Tostring
This expression is based on the Length of the string (number)

Regards
Gokul