I tried to give blood ONCE and found out that I was ineligible. For the next five years or so they harassed me non stop about giving blood. I told them I was ineligible they just said "ok" but I still got phonecalls. I asked them to stop calling me but they didn't stop. After a while I would just hang up on them. I got the phonecalls to stop by emailing the ombudsman. Never got a reply but the phonecalls stopped shortly after.
I recently decided to stop giving them blood, however, because I was actually reading the fine print for once, and apparently they send your blood off for use in research at universities and you cannot opt out.
Anyways, long story short, I will be using my local blood organizations from now on, or just going directly to the hospital to donate.
Thirty seconds later, the phone would ring again. "Hi, is Duncan there?" Repeat a third time for my other brother. For years. I think it's stopped now, so it didn't quite last a decade (though maybe it did for my older brother).
The Blood Center of Central Texas, on the other hand, stopped calling the first time I asked them to. Once they stopped, I resumed donating regularly.
All that aside, I highly recommend donating blood regularly--it has health benefits and is a pretty effective form of charity.
I redirected it to Google Voice and configured their numbers to go straight to voicemail. I figure if they have anything important to tell me, they'll leave a message.
They are also borderline abusive with how often they will call you and harass you if you miss an opportunity to donate blood. They apparently have unlimited funds to pay phone operators.