My mother just screams at the phone until the problem is solved. Sometimes i fell sorry for the person in the call center of my ISP.
... i love her 
It works here in Malaysia. 
That is real mean, most of these techs are working minimum wage exc. Anyhow on to the real question...
Naru you have been lied to and the techs don't know what they are talking about. First of all there are many things that can slow your connection down
now what worry me most is the one tech that said "Oh the signal is very weak." That automatically should mean a truck roll and a tech to your house
providing that this tech is not making shit up. The thing is when you have a weak signal you will notice packet loss. A easy way to check for packet loss
is to simply do a ping -t google.ca or something and if it starts timing out you have packet loss. Now the thing is that it can show as a weak signal for many
reasons though and there could be any number of reasons it could be as simple as a bad connector or a bad splitter. In fact while we are on the subject of
splitters there is something that should be a few things said on this topic as well. A cheap dollar store cable splitter is never good and should never be used
the problem would be getting your hands on some quality splitters either digitap or antronix. Now we can get to cable you should not have any cheap cable
used as it will have problems you should be using a rg6 cable like cable from belden. Oh my so much to explain still. The other thing is your cables should be
made up with compression fittings and done properly not falling off. The thing is the drop (line coming into the house) Should be split with a quality 2 way
splitter and each leg should get -3.5db anyways one leg of that splitter should go to the modem, then the other leg will usually go to another 3 or 4 way
splitter for tv service although sometimes cable networks aren't configured that way but im not even getting into that whole mess as to the other ways
of wiring and splitting. Anyhow i hope this is all making since here for you because after all this is checked if the signal is still not good then it could be
the modem. Now the problem is to isolate all this you need to test the signals and such and the fun thing is i have no idea where you can get a cable tv
tester as they cost a load of money and its probably cheaper to get a tech out to isolate this. Now the other fun thing is that it could be the drop coming
from the tap (that is where the cables get distributed from the main line) also aerial drops are prone to more problems due to wind, weather, trees, people,
exc that copper inside the cable can crack especially if its super cold and being blown around. Okay so lets now say that you arn't having signal loss and
that the tech you talked to just didn't know how to explain stuff basically you have what is called a node, a node will service lots of drops and this is where
the fun begins. The node may have a ton of subscribers and basically going to the node can be fiber maybe a t3 though unlikely dosen't really matter
basically that node has limited bandwidth and the isp banks on people not using all the bandwidth at the same time. This is why cable is prone to slow downs
especially if the node is packed full of subscribers because then what they have to do is a node split which is fun because that takes months of planning
and work and that is unfortunately never a overnight thing. The reality of it is that if its a node split im sure they know about it because they are probably
getting ppl calling in saying they are getting slow speeds and the fact is they are unlikely to actually admit it because guess what it means they messed
up and oversold and are getting complaints now. Also some modems have a page where you can access there diagnostics the address for that is: 192.168.100.1
Hope this helps and good luck on it all.