LTE network connection issue

Hi experts. I am facing LTE connection issue on my NightHawk MR1100 hotspot router. I am using STC(saudi Telecom) sim card. For the first 3 weeks it was connecting to LTE network and speed was good. After 3 weeks or usage, suddenly it stopped connecting any LTE band. When i choose auto mode, it connects to HSPA/3G but when i put it on LTE band, it fails to connect. Same simcard is working fine in smart phone or in other router. I changed the simcard and put another one of the same network but still it has the same problem. It connects to LTE band of other network like Zain network but only STC network having this problem.the apn set for the stc network is also ok (jawalnet.com.sa) as per their website.
Can anyone help me to solve the problem. 
i did factory reset but still it has the same problem.