The only thing i can tell you is that someone from Guinea is miss-calling you...
As far as I know there are multiple case where someone miss-calls and you call back and then your phone load is gone or you get charged a lot if you have a subscription.

But as far as i know, now there are security measures in place to prevent this from happening. But that doesn't mean that they do not happen anyway :)

Just be careful and don't call back.
Send an email to Qtel or Vodafone and tell them about your problem. Normally they should be able to help (block the phone number from calling again).

I'm not sure but i think you can also do that from your phone...