Not able to receive calls with softphone on Android

Hi gang, I use Voip.ms as my voip provider and also on my cellphone. I was using Zoiper to make and receive calls, but 3 weeks ago, Zoiper is unable receiving calls. I'm able to make calls but not receive them. The same with the other android app that I tried, Linphone. But when using CSipSimple, I can make and receive calls. What is different in csipsimple compared to the other android apps that I'm able to make and receive calls? I didn't change anything in my Voip.MS account. Thanks