Ripp off merchants !!!!!

Absolute nightmare company !! After agreeing to a special offer for facebook advertising (after a hard pitch sell) of £99 this went ahead ! What a pile of rubbish !!!! The advertisement they put together was absolute pants ! My 4 year old is more creative I had no hits or no increase in business ! In fact I don't think they could prove the ad even ran !! All you receive is a link to the ad ! Ah well I thought its only for a month ! Ha ha alas NO it wasn't until I received my credit card statement that I realised they had taken just under £300 off my card ! I contacted them and they told me that I had to cancel the contract (what contract I never agreed to) within 30 days and that it was to late to cancel the next one as well ! I had to cancel my credit card to make sure they didn't get any more money !!! Then the nastiness began ! Some awful woman talking to me as though I was 5 years old , awful to deal with unhelpful , snydey, I sent an email pointing out my concerns and that I didn't want any more adverts , to wich they said they never received ! Surprise surprise ! They sent me numerous emails and phone calls from accounts eventually thins died off ! But now over a year later I have now received a debt collectors letter claiming I owe them £590 ! So my nightmare begins again !!!
AVOID LIKE THE PLAGUE !! Any advise would be gladly appreciated
Answer IT should be investigated !!!