Reimbursement from Coop for funeral bill not forthcoming

Hi there,
My wife's mother died recently and her brother paid the bill for the Doctor's certificates (£164). This was in March. The lady at the Coop Funeral Care told my wife that this was clearly covered in the pre-paid funeral plan and that therefore we would quickly be refunded. Although she has requested (repeatedly) that the main office reimburse my wife's family for this, nothing happens. When we try to call the main office they blandly reassure my wife that we will be refunded, but nothing happens. What is the best way to pursue this? Is there a complaints procedure? It has cast a shadow over the whole service given by the Coop during what has been a distressing time.