+1 on the correspondence being in English.
Those BAK charges etc are nothing to do with who installed it, but they are the Cablecom hardware and connection to your apartment, and nothing to do with your subscription. Depending upon what is written in your rental contract for your apartment you may be responsible for this quarterly payment. We were in the same position and have to pay it, and our rough translation of the clause is " Cablecom is connected to the building, if you wish to make use of the service you will pay the appropriate fee directly to Cablecom, and your are responsible for arranging your contract for phone/tv/internet with them. If you do not wish to use the Cablecom service contact Cablecom directly and they will come and seal the sockets so they cannot be used and you will not be charged". Friends who rent in town who have also have Cablecom don't pay BAK as it's is covered in there rent or NK.
So the bill isn't erronius, as the nice sales guy only arranged your subscription. You need to speak to the rental agents about the BAK charge.... good luck with that, you may just have found you've been Switerlanded
