Is there any website service that will monitor packet loss for a long period of time. Current I am not too happy with my existing provider's network. They seems to have quite a lot of packet loss every couple of days. I just need some sort of proof so they wouldnt reply to me: " there is nothing wrong from where we could see".

Just use 'ping' to ping a few popular web sites in different times. And run it for at least five minutes each.