The bereavement service were very helpful, they got back to me straight away. They didn't have a record but suggested trying Grenoside crematorium. I've called them and they have confirmed my Great Aunty Bet's ashes are scattered there. She was moved from her flat a few years ago and we didn't have any contact details for her and then we found out at the weekend that she had died in 2016. At least now we can go and pay our respects.