Telephone country codes never begin with zero.
Telephone country code +21, dialed as 00 21 from many places, is an incomplete code in Africa. You need the next digit.
Telephone country code +1, dialed as 002 1 from many places, is North America (USA, Canada, etc.).
To reduce the possibility for confusion, it is best to quote an international telephone number beginning with the single plus symbol and the correct telephone country code.
(The plus sign means "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.