PC bug repair.com Systems tool? Computer held Hostage until I paid , Internet

I was on the computer one night and the computer screen had a page on it that said my computer was infected with viruses, trojens etc. The computer was held hostage, in a total lockdown till I paid this company to clean it. I did pay and they scanned what they had installed into my comuter to begin with and I wa able to get back on. I had been receiving messages saying that my free pc cleaner was expiring for a while but I knew that wasn't the case. When this happened, I figured I was wrong. After one day...systems tool dissapeared from my computer. I have the email with all the information that they sent me. When I tried a few times to cancel, being that they had a 30 day cancelation window, I got the run around. I then decided to research the web about them and see that I am not alone in this rip off. After I paid them the money, my usual anti-Virus is still in working order so all those messages I recieved about it ending were just to get me to pay them.