It can be really stressful! Had a stalker constantly ring and text my phone a few weeks ago and had to get a male friend to call him and ask him to stop....The stress of it! Problem was he started to call from private numbers too so I couldn't tell who it was...He's gone now...thank goodness but it aint nice!
You will need to involve your mobile phone company to block the number completely, and this may involve supporting documentation (Garda report in the case of stalking/malicious calls etc).
An alternative, if less satisfactory solution, is to assign the number you don't want to answer to a profile in your phone and then define the profile so that calls or texts from that number don't have an audible ringtone and are easier to ignore. Most phones allow this, but of course it's not much good if your caller is leaving messages or if you don't know their number.
Actually on a related matter, I believe in the US you can refuse to accept callers who block their phone number i.e. it doesn't even get to you, and they get a message saying for them to unblock their number before the call will be accepted. Pity we don't have that here.
not ideal, but, at least a fwe years ago, if you reported nuisance calls to the boys in blue, and if you took a record of same, the mobile phone company would give you a new phone no, free of charge. most mobile co's give you free on-line texts, you could just send a text from their website to everyone saying you've a new no.
Networks don't block incoming calls , however some handset do !!!
Samsung Zv10 has a auto reject list which can reject selected numbers or even private numbers
Nokia 6630 , 6680 , N70 (any symbian enabled handset) can be downloaded with software to do the same , although a small fee is involved (free trails available before purchase)
see - www.my-symbian.com