Do not bother ask them to explain who they are or how they have your number... Supposedly I registered with them even though I have never heard of them and do not give away my phone number easily.
In this most recent call the lady answered my request to be taken off the call list with "but of course it is normal to reject something you do not know anything about, But today might be your lucky day..."
Asked them several times to take me off their call list but I keep being called from diff