Contract cancelation for moving out of germany

Hi, good day! 

I was an AuPair in Germany and I let the company know about me coming back to México a month before, so I asked for a cancelation of my contract. I was asked to send paperwork and to pay a 3 month fee (which I did) but the paperwork was sent after me leaving since I needed a paper from the Rathaus about my deregistration and a letter that here in México we do not get once we are back in the country, there is not such a thing as registration of me to an apartment since I live with my family. So I sent a letter signed saying I got to my house and a copy of my ID (there you can find my adress). On Wednesday I receive a bill of the month of August and there I could see the 3 month fee payment I did, but I haven’t receive any confirmation of my contract cancellation saying that it is done and I don’t have any more charges. 

Could you help me with this, please? I am afraid my contract is still running and I would like to know the cancelation is at least in process. I need answers, please. 

Regards,

Sofia Muñoz