Phone

[long2019]

EVERY NIGHT AT 3.30 AM I GET A MOBILE CALL SOME TIMES ITS A PRIVATE CALLER
THEY DO NOT ANSWER
I THINK SOME ONE IS WATCHING
HOW CAN I BLOCK THE NUMBER

[sddsddean]

Just switch your phone off at night!

[Old_Geezer]

Beat me to it.
Or use an app that recognises the calling number and rejects the call.

[Maydup]

Without knowing your particular phone settings, try looking at the recent call. Highlight it and see if there is an option to block calls from this number, or add this number to reject list - something like that.

[fiction-factory]

Presumably the calls come from more than one number as you say "sometimes it's a private number". What other types of number do the callers have?
Are these calls to your home phone or your mobile?