Removing Drive Belt Pulley from Zanussi Washing Machine?

The drive belt came off my Zanussi Aquacylcle 1000 washing machine - Model Number FLA 1002W. I purchased a replacement belt, but it would not stay on the pulley wheel, which drives the drum. The pulley wheel looked badly worn and flat.
The new drive belt simply came off at the back of the pulley wheel whenever it was turned.
I tried to get the pulley wheel off but it was firmly fixed even after removing the holding bolt. Can anyone advise how to get it off so that I can replace it?