After twenty minutes of hold time, the system gave me an option to input my own phone number and have a representative call me back when it was my turn to be called. I decided to try that. I entered my number and the system kicked me off the phone.
Then I waited.
After about an hour or so, I decided that since the drive shafts were such an inexpensive component, I'd just go ahead and buy a new set. So $10 after shipping and I had a new pair of drive shafts on the way. That way I have one to replace the broken on and another one just in case something happens. I'll also have the nice metal drive shaft rings to make sure the problem doesn't occur again. I should have all of those parts by Saturday, I hope, so that I can get some good driving time in.
About an hour after placing the order, I got a call back from Horizon, finally. The guy on the phone was really friendly and apologized several times for how long it took them to get back with me, explaining that he was working overtime to get caught up on the calls. I told him it wasn't a big deal, and let him know about my broken drive shaft. I told him that I had the upgraded motor, and he told me that once I installed the optional motor some of the warranty doesn't apply, but he'd be glad to send me a new drive shaft set regardless. Cool. Now I have another pair of drive shafts coming, free of charge.
This way I will have THREE extra replacements after I repair the broken one...which should get me plenty of drive time.
I did fix the shaft again today in order to get some time with it on the road. I'm 100% sure that the car is running in the 25mph range now, if not quite a bit faster. It's awesome with the upgraded battery and motor because it flips itself over easily. I wheelied and flipped several times today before the drive shaft was thrown again. It's awesome!!!!