Default SKT LG G2 F320S not works with 3G and 4G in Russia

Hello! Could you please suggest me?
I bought the SKT LG G2 F320S phone, but WCDMA and LTE not works at all, although my operator(MegaFon) uses WCDMA2100 and LTE2600 frequences, that this phone supports and my usim card works good in another phone. Now I can only use GSM and data over GPRS... Maybe, it is qualcomm modem hardware problem? People on forums tells me that their phones F320S and F320K works fine in Russia... Do you heard about such problems? I use a stock ROM F320S11g with all updates and without rooting. Now OS version is KitKat 4.4.2, and ROM is F320S21d.