"Mistreatment of my mother "

My mother went into Milton Keynes General Hospital in Dec 08 for a knee replacement. Already a Parkinson and cancer patient she was not in good health. Five days after her operation at 2 am she pressed her call bell to go to the loo. After 30 mins a nurse came along to my mum, ordered her to get off the bed (shouting nastily), then threw mum into the bedside chair and left here there until 7 am. My mother wet herself after numerous calls and bells to the nurses. The rest of the ladies in the ward also pressed their call bells but were totally ignored. Finally, the woman who was in the bed next to Mum ordered a nurse to come and see to my mother and also called me at home. We rushed to the hospital to find my mother highly distressed and when we questioned the staff, of course they had no knowledge of anything at all. The matter was reported to the Matron. After chasing him 9 times, I finally got a letter. The nurse had denied everything. The letter made no sense at all and as far as they were concerned the matter was closed. So, in other words all this had been imagined everyone in the ward! I really dont know how to take this matter further and would appreciate some advice.