Why was I debited full amount and not pro-rata

I'm a rain subscriber and I'm writing this with disbelief, recently changed my debit date from the 25th to the 1st of each and every month and instead of them taking pro-rata they take the full amount, so it means now I paid twice for the same month and what's worse their consultants say they don't know what to do, like guys how, please tell me how, I need my refund minus they pro-rata please ASAP, also taking this to all social media platforms if my case won't be resolved.