Don’t call back any international unknown number
Don’t call back any international unknown number that comes from a country where you have no relatives or friends
When you call back these numbers, the call is transferred to a number of a certain company or service of international chatting programs. This is similar to the global chat competitions channels and programs with 0900 prefix, where an amount of money ($ 5 to $ 10) is deducted for this service, which you have been referred to.
Foremost of these numbers that you can call are the numbers with 876 prefix which is Jamaica country code, 473 prefix, that is Grenada country code, 287 as country code of Virgin Islands, 809 as the country code of Dominican Republic or 960 as the country code of the Maldives country.
You receive these calls randomly because some people might call back out of curiosity, hence when you call these numbers the line is opened and you hear strange noises, so you are forced to concentrate on them to understand what is going, so several minutes pass then find that your credit is stolen.
Moreover, don't ever respond to any e-mail messages from unknown persons or even known those emails that come from senders known to you (because that email account of a relative or a friend might be hacked). Such emails might inform you that you've won a prize that you should send your account number or call an international number is to inquire about your prize. In case you respond to these messages it ends up stealing your bank accounts and your credits or at least have your mobile credits stolen.