It's mad to me that you get to third year without understanding the difference between co-operation and collusion. It is not the University's job to continually inform you, it is incumbent upon you to know.
Any appeal would, I am certain, fail. It's cut and dry academic malpractice, unfortunately. In 3rd year, you are lucky it hasn't been escalated further and I really think that you have got off somewhat lightly. Take the win.