The truth about so called unlimited international calling

I was using international calling today and got disconnected after 19 minutes on call, then I couldn’t make a call for 30 minutes and then it worked, but again only for 19 minutes…I needed to reach a foreign carrier but couldn’t because I haven’t even been connected to an agent in 19 minutes…When contacted their support they said that it is normal…I get that there has to be a limit for how long you can be on a call, but 19 minutes is nothing…