I'm sick and treated terribly

Last year I went to collect medication which was owed to me. I was accused of collecting it but did not sign in their book for it. After the manager shouted at me publicly another staff member found it and apologised. The manager never did. Then recently a staff member said he would order medication for me and call me when it arrives. He never called and when I confronted him he said he never said he would call and didn't bother to get the medication. I told him it's the 2nd time I've had a bad incident. He then said why don't I go somewhere else if not happy. I told him I'd have to pay higher levies elsewhere as they are a designated provider for my chronic medication. After referring it to Donald the area manager he said he didn't think his staff need to apologise to me and they will be strict about my medication and if I place my complaint on the Internet they will write something back about myself. Should sick people with chronic medication be treated this way. I feel they have been very abusive towards me. Donald also asked me why I rather don't go somewhere else. I suppose that would be easier for him then to sort his staff out. I feel very hurt and humiliated.