Their servers are pretty unreliable and they seem to take forever to fix things so it's not a big surprise. It's most likely a temporary problem with the servers closest to your area. With premium though, you should be able to open multiple connections to the same file which is why they recommend a download manager since it can open a lot of slow connections to make the download go much faster.
I've heard Internet download manager is pretty good at this kind of thing so you could give it a try, jdownloader doesn't open a lot of them(although I don't have premium so I can't tell for sure).
When you contact any tech support to solve a problem, you want to give as much information as possible to help them solve your problem. If you don't, they'll give you the most common answer to the problem which is what you experienced.
They are pretty bad at responding though, I contacted them a few times with very specific questions and got a generic answer that didn't make any sense for what I asked about 2 out of 3 times. So try to email them 2 more times and you might get a good answer.
I haven't experienced any slowdown recently around here, it's still between 30 and 60 KBs.