incorrect billing

We hired a oxygen concentrator from ecomed on the 17 October 2014. Their monthly hiring fees are R750.00 per month. We paid the R750.00 on the day for the month, they then billed another R750.00 on 1 November 2014. When the payment of October was queried they advised that they do not pro rata any payments. None of this was advised when the machine was collected. We never received any statements from them and on 5 February 2015 they sent a statement which showed an arrears amount of R3000.00. We werent able to make payments as we never received any invoices or banking details. The fact that they billing a full months fees for a period of 13 days is ****************.