Server blocked for one network

Dear users , I have a cloud server which works fine at my 3 branches . But suddenly it stopped working at one of my branch that is in that branch if any of the sites under that server loaded in that branch it says either site can't be loaded or page not loading or server not found. at first i thought that that network ip might be blocked at firewall and so searched at firewall but that ip is not in blocked list .for one crosscheck i even tried flushing the firewall blocks but found no lucks. Kindly help me .