Frustrated

For the past month or so I have been experiencing a very bad internet connection.
Almost every evening my internet goes offline many times per hour, sometimes during the daytime too. As I have an internet business which I run from home, this is unacceptable.
As usual, Sonera will say there are no problems.
Some two weeks ago a technician came to my home (I did not even ask for it), and he simply took the cable out of the splitter (which was shared with the tv cable) and put it into a separate socket which he said was for 'data' only.
Basically, it a separate plug, like there is one of tv and one for radio. But anyone who has actually looked inside such a plug, knows that the wiring is all the same, it's one and the same cable which goes to all of those connections. Especially when you are talking about a building from the early 1980's, you cannot expect separate 'data' connections in a building of that age!!
So needless to say, after his 'fix' the problems continued.
Almost every evening I experience internet problems, just at the time when it is most busy for my business.
It's gone offline some 3 times so far while I have been writing this message, and no, I am not a slow typer!
The fault service suggest me to have my modem tested in a Sonera store. I will do that, but I highly doubt there's any problems with the modem, seeing that this only happens during evenings.
My guess is that the network is saturated in this area (Rovaniemi). I hear other people are having problems too, so obviously it is not just me.
Hoping that this will be solved once and for all soon!!