The most likely answer to this is that the company is quoting only the national dialling code / phone number for calling it.
So as per the 1st answerer, you need to know what country it is in, look up the International Dialling Code for that country using the link Eddie gave you, delete the leading zero off the number so it then starts with the '1' then dial the whole lot.
As a clue, many countries still use '01' for their capital or largest city - as did London until we ran out of digits a few years ago.