Openreach LOS in red

[Chor+Yan]

the LOS light occasionally off or red. No any internet signal. Anybody can help and who can I contact? 
please

[Highlinder]

@Chor+Yan  Are you in the UK or Ireland? Are you able to call Sky and report this fault to Sky?

[Chor+Yan]

I'm in UK

[Highlinder]

@Chor+Yan  Can you please run the broadband test, this can be done either via the Sky app on mobile data or use the link below.
https://www.sky.com/help/diagnostics/sky-broadband-diagnostic/sky-broadband-diagnostic

If it finds an external fault it should enable you to book an engineer.

Do this when the issue is going on. It looks like an external issue, but you have made sure that the ONT is connected properly, that is the green fibre cable is connected and seated properly.