Faulty Samsung S6 Edge

I am an Ear, Nose & Throat specialist in Private Practice. My phone is always diverted to voicemail due to the fact that I am either consulting or in surgery. I upgraded to a Samsung S6 edge in 2015 and within a short time there was no notification to show a missed call or voicemail message left by my patients. I have sent my phone in numerous times and each time it came back with the same issue. Out of necessity I have reverted back to my old LG phone due to the fact that very serious issues have arisen as I never received my patients voicemails. Please advise on what next steps should be taken. Thank you. Dr Henkel.