Help on using AT&T Samsung Note 3 SM N900A with Waridtel 4G LTE in Pakistan

I have just received my AT&T Samsung Note 3 model SM N900A and am using it in Pakistan with warid network. I received the sim unlock code from AT&T. Warid is giving us 4G LTE service but my cell does not work on it. Since warid is not giving 3G service, my cell just connects using edge which is very slow. I actually bought Note 3 for 4G LTE but due to some reason its not working. The carrier people have no answer except that my set is not supported by their system. Can you kindly help? My set is not rooted.

Warid 4G LTE is working on 1800Mhz FDD Band 3 which is supported by my set. Other device parameters are as below:

Baseband version N900AUCUBMJ5
KERNEL VERSION 3.4.0-1625098
se.infra@SEP-121 #1
build JSS15J.N900AUCUBMJ5
Android version 4.3

And I would also like to know if I can update my set to newer android version or not?

Awaiting your positive response.
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