I planted seeds for 3 varieties of sunflowers: autumn beauty, mexican, sunspot. I'm not sure which but one of the varieties just grew and kept growing and did not flower. At this point, it is over 5' tall, with a healthy tick stalk. My problem is that I have a screen enclosed garden so it's butting into my "ceiling". There's only one place for them to grow and that's making a u-turn and coming back down, which I'm not sure they would survive. I've read that planting sunflowers close to each other makes them grow instead of flower but I'm beyond that at this point, they are pretty established. Should I prune them to start over? Above or below a branch, and which branch at that? I'm new to flowers so I appreciate your advice. Thanks in advance!
Sunspot is a relatively "short" variety that only grows to 4 feet. Autumn beauty will grow to about 6 feet. The Mexican sunflower Tithonia diversifolia (which is not really a sunflower at all, though it looks similar) grows from 6 to 10 feet tall.
I think your plants are just doing what they do, and you chose the wrong plants to grow if you have limited height available.
You can't prune annual sunflowers like sunspot or autumn beauty. You only get one large flower at the top of the stem. If you prune them you won't get a flower, and they might just die.
You can prune Mexican sunflowers (cut off about 1/3 of the length of the stem) but you will reduce the number of flowers. It would have been better to prune them when they were smaller, of course.
You can get "dwarf sunflowers" that are often grown in pots and containers, and are about 2 feet tall. If you want to try again next year, make sure you are buying those varieties.
I noticed there seem to be a lot of sellers on EBay, Amazon, etc offering a mixture of sunflower seeds of the three varieties you mentioned. It is usually better to buy from a well known seed supplier (or from a garden center) than from "some guy on the internet." You will get accurate information about what you are buying, and you are more likely to get seeds that really are the same variety as the label on the packet!