I had the same problems last summer (at the time I had an eircom line and phone calls via Chorus), and despite telling the caller that I didn't want another call, they kept on coming! Even had a person at the door one evening!
I sent a complaint (via the eircom website if I remember) and said that if I received one more call, I'd switch providers immediately....the calls stopped funnily enough! (then I switched anyway!).
SlurrySlump, do you pay eircom for your line rental or do you pay BT for the lot? (I'm a BT customer with broadband and only get one bill from them, nothing from eircom). I ask because there's an option on the BT website to opt out of all cold-calling - which all companies are supposed to honour.