My phone balance deducted!!

I’m from Egypt and I have an Etisalat number, I had charged a balance with 10 EGP, and from time to time I receive a message that say that 2 EGP was deducted without any reason for that!!

I called the customer service of Etisalat Masr and they said that there are an international messages was sent from your iPhone, when I said that I didn’t sent any messages they said that the problem may be from FaceTime app, I disabled the app from the settings and such apps like iMessages.

the problem is today I charged a balance with 10EGP and the iPhone was sent a three international messages and every one was charged my balance with 2EGP!!

could you please help me stop this messages, because it deducts my balance??