I had a minor accident. I was backing up and lightly hit a pole. The left rear wheel won't turn

The impact has damaged something and only an inspection would tell you what is wrong and requires repair/replacement.

It should be something to do with the suspension system and wheels.

What do you mean by "won't turn in unison with other wheels"? Turns at a different speed? Different direction? It sounds like the left rear spindle is bent and that wheel is steering to the right. That makes the rear of the car go to the right and the front steers to the left. You have to compensate by turning the steering wheel to the right. You're turning the front wheels to match the rear wheels.

On an alignment computer it is the left rear "toe" that will be wrong, and that means "total toe" will be wrong. Total toe simply looks at the two rear wheels together and that number is critical for good tire wear. Right now your rear tires are pointed closer together on the their fronts, kind of like a V-shaped snow plow going down the road. That is going to scrub off the tire tread on both tires. You'll see the horrendous wear patterns on both tires equally if that isn't fixed.

I shouldn't have assumed the spindle is bent because that actually takes a pretty good impact. In an effort to make cars lighter many manufacturers have gone to really flimsy little suspension "links" or bars that hold the rear wheels in position. Some of them are so weak they can be bent by hitting a mosquito! Okay, that's a slight exaggeration but normal driving is enough to constantly be throwing those systems out of alignment. The ride quality is better than the older tougher solid rear axles but it comes at a price.

Yea make sure you get this checked asap. It can be really dangerous. Imagine if you are in suddenly in a tight spot and need to make accurate adjustments while driving. Be careful out there!