If for whatever reason the following doesn't fix your issue, join the Discord server and ask in the public channels only for help. Do not respond to any DMs as scammers might try to trick you into giving them your funds!
You can use the debug console to quickly add an official peer that is geographically closest to you by typing:
addnode node_ip_or_dns_address add
nix-cli addnode node_ip_or_dns_address add
ny.nixplatform.io (United States)
sf.nixplatform.io (United States)
ldn.nixplatform.io (England)
fra.nixplatform.io (Germany)
tor.nixplatform.io (Canada)
sgp.nixplatform.io (Singapore)
blr.nixplatform.io (India)