Disrupted DSL connection for the past two weeks.

I recently shifted to Heidelberg, Germany and took a DSL connection by o2. I got a Fritzbox 7490 from an o2 outlet. The connection was established on the 18th of May, however, there was no DSL connection at my place for about a week because of a faulty connection made by the technician. I lodged a complaint with the o2 technical hotline and this took me about three days since no one was ready to speak in English with me and that is the only language I can communicate in because I have only recently moved to Germany. This problem was then fixed and I had undisrupted internet connection for about two weeks. 

From the 6th of June the DSL connection started showing some disruption again. The connection stays for 2 to 3 minutes and then goes off. There is undisrupted connection sometime at night after 10 pm but during the day the connection is always unstable. This has made working difficult for me and I’m having to recharge my handy with internet data everyday just so I can work. The customer care executives have been extremely unhelpful, refusing to speak in English and I have made multiple failed attempts to get my complaint registered. On the 16th of June I decided to take the help of my neighbour who speaks German and a complaint was lodged. o2 opened a ticket for me and I received a message saying that the ticket has been submitted for a technical check. There has been no interference suppression as of yet and the DSL connection at my place is still disrupted, however, I received a message from o2 yesterday saying that the ticket has been closed.

I have been unable to work because of the unstable DSL connection and o2 customer care has proved to be extremely unhelpful. The ticket that was opened has been closed without my problem being solved. I have also submitted feedbacks where I have mentioned that my problem has been left unsolved and yet no one has tried to get in touch with me.

The water is way above the head now, I have been paying for data that I have not even used and on top of that I am having to pay for mobile internet data. I would like an immediate remediation of my situation or I would have to think about contract termination with o2.

edit by Thomas3 : Question moved from “dig. Wohnzimmer” to “english forum broadband area”