Telephone country codes never begin with zero.
Country code +82, dialed as 00 82 from many places, is South Korea. A number beginning with +82 1 is a mobile phone from South Korea; however, it is incorrect to refer to "country code +821" or "country code 00821"; the correct country code is just +82.
Country code +21, dialed as 008 21 from many places, is an incomplete code somewhere in Africa. You need one more digit to specify the country. For example, +211 is South Sudan and +216 is Tunisia.
To avoid confusion, it is best to write an international telephone number in correct international format, beginning with the plus symbol and the correct telephone country code (e.g., +82 or +216), omitting any dialing prefix.
(The plus signmeans "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
0021 is not the country code for England. England uses the United Kingdom country code +44 which is dialled as 00 44 from most of Europe or 011 44 from North America.
Leichtenstein is telephone country code +423.
where is telephone country code 1816
That is not a country code.
Country code +57 is Colombia.
Country code 52 is Mexico.
Fiji has telephone country code +679.
Gibraltar is country code +350.
Moldova is country code +373.
Slovenia is country code +386.
Vanuatu is country code +678.
Niue is country code +683.