Broken Drum Belt on Hotpoint WM64?

Hi

I have a Hotpoint WM64 washing machine which the drum belt has broken on. Never having opended a washing machine before I thought I would have a look inside and see if I could put it right. I have taken the top off and the bottom panel and the small hatch on the back I took the broken belt to a spares shop and they gave me a replacement.

The problem is the belt will not fit round the wheel on the drum and strech to the motor at the top. I have tried losening the nut that holds the pump on and pushing it closer to the drum but this hasn't helped.

The old belt was labeled - Hotpoint No: 161609 (4299) with a 6 on it.

The New belt Contitech PJ1245/490J EL (1653) with two 1's in green.

The new belt seems to be about 3cms smaller in size but I guess the old one could have streched is it possible the shop have given me the wrong belt even though they looked at the old one or am I doing something wrong?

Thanks a lot for your help.