There are tons of threads on this subject if you search for cold toes/feet. It sounds like you are using "summer" cycling shoes in the winter. This doesn't work. Most cycling shoes, including most that are designed for winter are too narrow in the toe box.

If you can't easily wiggle your toes, your shoe is too tight. Space inside shoes + warm socks = warm feet. I'm talking LOTS of space here. My Lake MXZ 300 winter boots suffer the same problems. I can wear them down into the teens with an oversock, but they are cut too tight to be as good as other options.

I wear a pair of thinsulate hiking boots and use platforms when temps get down in the single digits and below. These boots are almost 3 sizes too large for me, but ideal for winter cycling. Because my feet have tons of wiggle room.