This was apprently resolved, and indeed I could again access sites that I wasn't able to get to before. But the day this issue got fixed my connection went down due to, apparently, a central-NI wide failure at Telecom. My connection was down until about 10pm on Monday.
It's now back up, but I'm continuing to have some pretty major problems. A lot of sites are failing to finish loading, including, for example, facebook, which has various broken images every time I load it, and Chrome gives me a continuously spinning circle. I'd had similar issues on other websites too.
This is frustrating - I chose telecom because despite being the most expensive ISP, they were supposed to be the most reliable. Reliability means more to me than anything, but this is ridiculous lately. Anyone know what's going on?