have called the number to buy credits, but it is not working

The number that you call is a premium number. It is possible that the policy of your land line or mobile operator is to block such numbers as a default setting. In case you cannot reach the service, please contact your operator and request unblocking the premium numbers.
If you are sure that your line is not blocked for premium numbers and you still cannot purchase credits, please contact the Helpdesk. Mention your own number, your operator, and the exact time of your call to our premium line.