Help finalizing contract cancellation

I was told to come here from O2 Facebook Messenger to further cancel my contracts. I cancel my four o2 handy contracts on 25 Jun 18. All four. For some reason I keep getting billed for one of the four. Before I left I contact o2 by phone and went into local o2 shops and was assured everything was in order. However, I keep getting billed after leaving Germany for over a month. I'm at the end of my rope to cancel this contract finally but o2 belabors this process to no end. It should be simple but o2 has made it beyond difficult to cancel where as I gave them 45 days prior to my departure to cancel and I was charged for canceling before contract expired and paid. Please someone from O2 hear me and reachout to assist. PLEASE!