anonymous call blocking

[#1]

I signed up for anonymous call block  Im fed up with getting sales calls.
It's not working just got one, pressed 147 and got 'we do not have the callers number to return the call'
If it was a free service I wouldn't worry but it costs £4 a month
What should I do?

[#2]

Anonymous call reject won't block every call where the number doesn't appear, have a look here for more info:
http://www.plus.net/support/phone/call_features.shtml#reject

[#3]

Get something like cpr call blocker, which does more than you want for a one off £39.99 - less than your current yearly spend You will, however, need "Caller Display" for it to work - so your actual savings will start after 13 months :'(.
Though not a recommended layout, it successfully blocks calls with three phones, including a "1571" indicator phone, and the blocker at the end of an extension to one of the phones

[#4]

Have you signed up with the TPS?  We get very few calls now, certainly not enough to make £40-£50 worth spending...

[#5]

@pwatson -you're the lucky one. I've been signed up to TPS for several years but the calls keep coming. 
I'm reluctant to use the cpr call blocker as some of the calls I receive do not fall into the nuisance category.