You can probably repair the antenna.

The problem is probably that the nylon cable is broken. Have someone cycle on/off the ignition with radio on and listen to hear if antenna motor runs. If it does, all is probably well except the mast itself.

Get a replacement mast (~$20).
Remove the trim nut that the mast goes through.
On the antenna up cycle, just pull on the mast as it attempts to rise, and you can pull it all the way out (keep pulling).

Compare the length of the nylon toothed cable on the replacement with the old mast. If they're not the same, it means a piece of it broke off (the likely problem) and remains in the antenna--you'll have to remove the antenna from the car and open up the motor box to retrieve it--this is not hard, just remember how it went. There is a trunk trim panel to be temporarily removed to gain access to the antenna--not hard either (turn the mounting plugs a 1/4 turn to remove them. The cable wraps around a pully and can be a bit hard to see, but the broken piece has to be in there somewhere.

My sons's Volvo is currently 60 mi away, so I can't remember orientation, but here's how to check. The nylon cable is going to wrap around a toothed pulley, and obviously the teeth need to be aligned to mesh. So, if the antenna mast enters the motor box at the front (of the car) stuff the nylon cable down the tube with the teeth facing rearward. If the mast enters at the back, stuff the cable with the teeth facing forward. Push down a bit, and have your assistant turn off the ignition so the motor goes into the retract cycle. The pulley should grab the cable and wind it up and retract the antenna. You need to guide it as it retracts so it doesn't hang up. You'll need to transfer a metal sleeve from the old mast to the new one (do before installation), and when it's all installed, refit the nut and rubber cover.