can't connect with 4g, only 3g

Dear friends, I have Nexus 5 but 4G doesn't works . My service provider supports 4G service at 800MHz and 1800MHz as it shown here http://www.gsmarena.com/network-band...ountry=Morocco , but my nexus 5 d 821 does not work with 4G, I want to ask that if there is a solution like a roms or others things.
Thanks in advance.