Yelling loudly at someone would make me feel better for the lost hour and a half of my life troubleshooting my connection problem earlier today. I'm not going to, because I understand that in most cases the helpdesk staff have no say over these decisions. But I shouldn't have to be friendly to the helpdesk just for them to remedy this, because (at least in my opinion) it's a breach of their obligations under the CGA to provide me with the same service they told me they provided in the first place, and have never told me has changed.
You clearly don't understand the CGA... It isn't a breach as by simply phoning them they'll make it right for you. No need to yell at the person at the other end of the phone - it isn't their fault and they're a person also but they'll be quite happy to help if you're calm and simply say "hey, noticed this service isn't working anymore".
Under the CGA they're still providing you internet and as you only noticed it maybe 3 months later it is clear your service was working fine.
Just don't be that person, it doesn't fix anything - if anything, it'll make the CSR less likely to help you out. They don't have to accept customers who are abusive to them.