Hi Tony, if your new company is professional, they should completely ignore anything that has been said to them verbally. It is only if it has been put in writing as a reference, that you should worry about it.
If you were so bad in your old job then why were you still employed by your old company? Why would your old boss put up with bad performance from you? Was he so weak that he could not deal with your 'poor performance' and the only way to get rid was for you to leave on your own basis? This whole situation only makes him look bad and shows him up as a weak boss.
You could try and take it further, either with your new company or your old, but it may just have the effect of looking like sour grapes with your old company and you looking like a trouble maker with your new one. Let your new company come to you, if they have any real concerns. This did happen to me with my last job. My old supervisor phoned up my new company and made an 'off the record' remark that they should not employ me as I was not trustworthy. My new company would not take it seriously unless he was prepared to put it in writing and as it was a complete lie, he could not do so of course! I ended up staying in my last job for 10 years, so I was not that untrustworthy!. I now own my own business and would not listen to any hearsay about my own employees.
Hope this helps, Sue