Make sure you are dialling the right number:
For a UK Merchant, if the phone number is
0207 xxx xxxx, then to dial it from overseas you need to drop the 0 at the beginning and dial
00 44 207 xxx xxxx or
+44 207 xxx xxxx.
For a US Merchant, if the phone number is
213 111 2222 then to dial it from overseas you will need to dial
00 1 213 111 2222 or
+1 213 111 2222.
Numbers which begin 1-800 or 800 are free call numbers in the US, and numbers which begin 0800 or 08xx in the UK are free call numbers. These numbers do not always work when you dial from outside the country. Or you may get a message advising you that the call is not free and will be charged at international rates. If you are unable to get through to your Merchant's free phone number , you should look for another number on their website, or send the Merchant an email asking for another number.
If you have a Skype account, you can make international calls using Skype credits.
You can find out more about international dialing at http://www.timeanddate.com/worldclock/dialing.html