Follow this list to diagnose the issue:
1) Dial the correct access number for your destination (noting that access numbers are usually different for calling landlines and mobiles)?
2) Did you enter the full international number (including international dialing code)?
3) Did you follow your international number by #?
4) If you heard a message in a foreign language, it is most likely a problem at the "other end" (eg. the mobile you are calling is out of coverage, or the foreign network is overloaded), try calling back a bit later.
If the above list doesn't solve your query, get in touch