Help "Weak connection" when video calling

[Jamie McGrath]

When I video call on my Galaxy A7 via the apps: Kakao, Line, and Skype I always experience a "bad connection" before it inevitably terminates all together. I don't use wifi - just my data plan. The strange thing is, I can download large files, stream videos, AND video call using Facebook Messenger without any hiccups!
How do I 'fix' the other apps to allow successful video calling?

 

[James L]

Have you tried Hangouts?

 

[sleedeane]

Or the award-winning OoVoo?