HD Voice calls problem

Cessio(Hungary)

Hi! My problem is, that since last update, when i use 4G connection (4G is the preferred network), and I start a call, the network drops to EDGE instead of 3G. On 3G I could make HD Voice calls, but now I can't. My SIM is from T-mobile Hungary. I already made a factory reset, but the problem remained the same. The HD Voice works on other devices, with the same settings, with the same SIM. What should I do? Is this a softwer issue?