Spam calls

In the last week i've been cold called four (4) times by the call centre trying to sell me their products. Each time i say 'no' and each time i ask to be removed from their database but the spiteful agents decide to leave my name there so that someone else can annoy me later. My name has been taken off the list at the DMSA but you still decide to call me. I am not interested!!!!! Please follow the law and please train your staff to follow instructions.