Welcome to Melita
Well here are the possible problems.
Melita blamed your computer and you, in a formal way ofcourse...
Your modem needs to be changed
Your coaxial cable (White Round Cable From Melita) has interferiance, which could be from a Television that is connected to it or maybe the cable is old. (TV before internet problem)
You need a signal booster (Installed By Melita)
The cabeling on the outside is damaged
One of those is usually the problem, this happens when you Modem exceeds the speed limit of your set bandwidth. For example I pay for 50MBPS but because of faulty wiring and I was getting a 100MPBS speed with loads of signal interference. melita changed my wiring setup (Connected my modem, directly to the outside melita box) and I got my 50MBPS speed with very little latency and loss.
I noticed the UPNP was resetting my connections all the time, since the PlaystatioNetwork used UPNP my modem used to reset all the time but now it's fine.
Call melita and ask them to inspect the 4 things explained above. OH! and yes forgot to say, Melita does those things exactly as I listed them. First they blame you for downloading too much with torrents and having not set you speed limit on your torrent client, then they come in and blame the modem thats not working properly. After a week period the problems come again and check you cabled and change them, if the problem persists they promise you to install a signal booster (never happens) and them they check the cabled outside and they say that it was their fault as the cabled on the outside 3 blocks away were damaged... For me the third step worked but my friend went past the outside cable problem. Eventually they fixed it though.
And that was my story!