Cancellation because of emigration not yet processed?

I terminated my subscription at the beginning of August as i left the Netherlands on the 26th of July and traveled back to my home country, i also sent a proof of de-registration from the gemeente of Almere, however i still got a factuur for the period of Aug16 - Sep15 for the amount of 53 Euros

Why am i being charged for this? Is this a mistake or will this be the last month i will be charged?

Thanks 

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