Regex to match a 2-digit number (to validate Credit/Debit Card Issue number)

You can use the start (^) and end ($) of line indicators:

^[0-9]{2}$

Some language also have functions that allows you to match against an entire string, where-as you were using a find function. Matching against the entire string will make your regex work as an alternative to the above. The above regex will also work, but the ^ and $ will be redundant.