Receiving unwanted email, I mark it as spam and a day or two later it reappears and there is additional spam?

Have you checked the spam section.Maybe it is full .Go to spam,click on mail,then again on addresses,see if your box has full 500 mails,if so then unblock a few and then check if the problem still occurs.Writing to yahoo is of no use ,they have the same Stereo type answers which are of no use.