Welcome to the community!
Where did you purchase your phone? Are you aware of the bands/frequencies your phone uses? There seems to be conflicting information regarding that model version of the phone. According to GSMArena, these are the phone's band/frequency specifications:
|2G bands||GSM 850 / 900 / 1800 / 1900 - SIM 1 & SIM 2|
|3G bands||HSDPA 850 / 900 / 2100|
|4G bands||LTE band 1(2100), 3(1800), 5(850), 8(900), 38(2600), 39(1900), 40(2300), 41(2500)|
According to those specifications, that phone has all of the bands/frequencies for 2G but only one compatible band/frequency for '3G'. With regards to LTE, that phone does not have any compatible bands or frequencies.
On the other hand, these are the specifications listed on SnapDeal:
According to those specifications, that phone has all of the compatible bands/frequencies for 2G and '3G'. With regards to LTE, that phone may have one compatible band frequency.
However, on these are the specifications from the Honor website,
4G LTE FDD: B1/3/5/8
4G LTE TDD: B40/41
3G UMTS: B1/8
2G GSM: B3/8
According to those specifications, that phone doesn't have any compatible bands/frequencies. Admittedly, the Honor website does not specify to which version of the Honor 8X those specifications belong.
You can verify the compatible bands/frequencies here.
I understand you noted that data and messages are OK. To which network was your phone connected for data? Are you able to use large amounts of data or only small amounts at a time? Are you unable to make/receive voice calls everywhere or only at certain locations?
Since it appears that most specification listings show the phone does not support the compatible LTE bands/frequencies, you might consider disabling LTE to see if that allows you to use your voice services. Have you verified your phone is using the proper APN? You can verify those settings here.
Hope this helps 😀