Call quality problems with Samsung Galaxy S5 Neo

[AC Question]

Hi. I've recently bought a Samsung Galaxy S5 Neo and some of my contacts are refering that my calls are not very clear sometimes. As I understand this is a common problem and I would resolve it ASAP... So, anyone can help to solve the problem? I'm not finding anywhere the option to cancel the noise reduction during a call!! I've read somewhere that it could solve the problem, but how can I find that option on the Android 5.1 ? Any help will be great. Thanks ;-) Regards from Portugal.