bottom line: you need a regular phone line as supplied only by Swisscom for ADSL.
I'd call Cablecom BILLING on 0800 330800 and bitch about it and see what you can get to keep you from going to the opposition. And I'd stitch-up the salesman at MediaMarkt - tell them the day and location and I'm sure he'll be spoken-to....
These plebs are all over and do try the hard sell. One tried it with me, Digital TV is the only thing I don't have from them and he was telling me about analogue switch-off etc etc. So I said I have Sky ("it won't work from 2010" - yeah right) and now I'd say to him "so can you offer me HD TV now, today?" and see the er squirm