Witheld numbers every day.phone rings i say hello it goes dead after about ten seconds?

no ones there or i answer and say hello its quiet and then there is a crackling like an interference after about 5 seconds .i used to get dodgy calls off a certain person over a year ago,dont want get a block on my phone again.as anybody else experienced theese calls or am i being paranoid,been every day now for over a month .cheers anybody xx