I haven't ever seen such slow download speed- nor have I ever seen such fast upload speed! That is really topsy turvy! (sp?)
But it can depend on which speed test you run. My 'speed' has never been what I am suppose to be getting which now is 15Mbps download. But for first time I saw 21.47Mbps down with a consistent 2.03Mbps up.
Upload speed stayed the same no matter which test I used- about 2.03Mbps, but the one test with 21.47down had Ping of 31ms! Go figure!
Did you use the speed-test recommended by the ISP? Did you compare it to any other test? Find out where the server is located for your ISP, then choose that location on test if you have a choice. Then compare the test. I use 6 different speed check sites and got from 21.47 down to 1.75 up. Big differences.
Time of day can make a difference as mentioned, but I'd be interested to hear what your ISP has to say about the numbers you got!