I know this is lengthy but please help me?

I recently renovated a property and one of my cousins said he knew of a person that disposes waste. So I rung this guy up and he gave me a price and said it would take him £40 to dispose it and he would keep the rest. So I thought he was genuine and was getting rid of it the proper way (in a waste disposal place) as he also had an open top truck. Now the council has accused me of fly tipping because that guy just chucked the rubbish on the street. The council interviewed me today and don’t believe in what I say. All I have is his number I was thinking of calling him again and recording the conversation and taking his photos. Does anyone have any advice for me as I might get a hefty fine for something I haven’t done. If I knew he was going to get rid of it like that I would have never given it to him.