Real simple, Small claims court. Even if it's $300.00. I once sued a company for $30.00, not a typo THIRTY dollars.
For me it's principal. Oh sure it cost me more in time and energy to collect, but the point is I won and they were forced to pay and I guarantee they will think twice before doing what they did to me with another customer.
I also sued a tractor repair facility. They quoted a price I signed and agreed to that price and at pick up time they wanted $250.00 MORE than what we agreed on. I refused and they would not release my tractor. I needed the tractor so I hired people to do the tractor work I needed while they held captive my tractor. I sued them for $3,500 or the amount I had to pay for tractor work.
They showed up in court stunned at the amount I was suing them for and at that time GLADLY agreed to charge me my original $500.00 repair fee.
Too late, the judge ruled in my favor and awarded me $3,500.00, plus no charge for the repairs in penalty for trying to screw me. They returned my tractor with a check the next day per the judge.
Do I hate suing people? Not as much as I hate being screwed by unscrupulous business people.