Incompetance & *****

Every second month i have problems getting my chronic medication. Discovery change my delivery from Optipharm to MedExpres. I called medexpress today to place my order and they told me that an order was already been placed by optipharm on the 6th August, I have been paying optipharm for the past year for my medication they still have a debit order going off my account even though my medication is suppose to be delivered by medexpress.When i called optipharm to find out why they claim for my medication and dont deliver it they say it is because i am in arrears and if i dont settle the account i wont receive my medication. How can i be in arrears if i have proof that they debit my account every month. I need a good laywer because medexpress and optipharm are playing russian roulette with my life. I need optipharm to cancel my delivery and allow medexpress to deliver my medication as in yesterday.