So where I am there is only one ISP to choose from , it had disclaimed once it does not favor VOIP apps because they are also a GSM providers and find that VOIP is a major threat to GSM calls where they generate most their profit .

Later on the majority of VOIP apps were blocked for use all over here except for three services and those are Facebook Messenger , Skype and Viber .

Yet as public started to complain , the ISP stated that it has nothing to do with this .

People filing ticket support received the very same answer from all VOIP apps , that the received VOIP packets from that ISP are corrupted somehow .

People started believing that this come to be some Glomar situation where the ISP tries to achieve their goal without violation of T.O.S

Suddenly the majority of VOIP apps on android came back to work , along with Sony PS , surprisingly nothing yet on Windows PCs which seemed strange to everybody .

Only a VPN comes to let all these services work again .

There is a catch we do not understand however , with every Cumulative update in Windows , complete availability to VOIP apps is restored for 3 whole days , then its back to the busted state .

I am trying to figure what is going on here , are there actually filters they can use to block Windows VOIP apps just ? or is it actually Windows fault ? Could there be a Winsock fix for this ? and why may cumulative updates and that phenomena be related

P.S I am not talking on just my behalf , this happens on a global scale
P.S2 I can not disclose more info