Does data have priority over voice when making calls on 3G? I'm not quite sure if this is the correct place to ask this, recently my phone service provider sent me a message saying that they had now begun compensating subscribers whose calls were dropped mid-call. They said their systems would decide if a call was dropped prematurely and if it was then we would be given bonus airtime. Prior to this, my calls never dropped and I didn't have much of a problem when calling. A few days after this I notice a lot of my calls keep dropping when I try and make them and after I make them. My signal is strong -full bars actually-but I assume 4G might be unstable so I switch my preferred network type to 3G only to prevent the phone from switching networks. This doesn't make much difference as my calls still keep dropping.

So I pass by their shop and one of their attendants informs me that the problem would most likely be attributed to the fact that when I make my calls, apparently data has preference over voice despite the fact that I'm not even using an app that requires heavy data/data at all when I'm making my voice calls. Before my service provider sent that message, I really didn't have much of a problem making calls but now it's become too much with literally 2 out of 3 calls getting dropped. So my question would be, when making voice calls, is data given preference over voice or did that attendant really not know what he was talking about.

For technical terms I have a galaxy s5(SM G900F) running android marshmallow. Never tampered with any of my settings.
Typical  4 bars on 3G has a signal strength of -81dBm 16asu
Voice and data are handled independently in 3G- voice uses circuit switching and data on packet switching. Hence, priority of one over another is not correct as claimed. For additional details see this

Frequent call drops could be due to other reasons like tower density, frequency used, congestion, Overloading etc, which can be addressed by your carrier. Your signal can be strong, yet you may face call drops or not being able to connect because of these issues