Getting Unwanted Mails on Gmail

Hello everyone! I use Gmail to receive and send e-mails. I have again and again marked certain mails from certain senders as spam. Not only that, I made sure that I had set up filters which would automatically delete e-mails which have a certain format/sender/subject. But the problem is that I still keep on getting mails from people with subjects I don’t want. How can I fix this problem? Please help!
