They made a mistake now I must suffer

I am getting a monthly income from sanlam. Last month they paid in an what was equivalent to 2 months income. Now they want to refuse a payment for next month even though I was willing to make an arrangement with them. This payment was made in error by them and there where no prior arrangement made by sanlam before the payment was made. Nou I have to suffer for 2 months and I have bills to pay. Last my policy clearly states that I will receive an income every month.