Penalised for cancelling cover

I recently cancelled my comprehensive car insurance with miway, giving them a month's notice on the 27th Sept. My premium had already gone through on the 25th September. On the 2nd Oct, I was billed R1 436.25, when I called I was told it was a mistake, I was still covered until the 26th Oct and the money will be refunded into my account. Today I got an sms that R1 066.87 will be refunded. Where is the balance? Why are customers penalised for getting better deals? Why was I even billed 'mistakenly' if you are not refunding every cent you took from me?