Sixt review: Car rental

I rented a car from Sixt in London. I rented the largest car I could find to fit my family of 4 and our luggage. the car I picked was a Mercedes E class. on the site and on my reservation the rental states 7 passenger with 6 bags. when I got to the front desk I got the classic "bait and switch" the front desk attendant told me the car I rented only sat 4 people with maybe room in the hatch for 2 bags, due to the fact that it was a hybrid. I showed him my reservation with the 7 passenger and 6 bags, he said the site was wrong. He said that the only car that could accommodate me was a much more expensive car. He told me that since I had the original stating the size promised that I could reach out to the management and they would take care of it. So I took the car. Managment said they wouldn't help because I agreed to the update. Even after I send them all the documentation to support my claim. Additionally, the car I got had a flat tire. I told the attendant that there was a warning light on the dash. He told me to ignore it and that the tire was replaced. It wasn't. Half way through Great Britian the car started to veer to the left hard. I slowed down for 30 miles and get to a rest stop. the tire was almost flat. I limped the car to Edinburgh to a Sixt location, the attendant found the issue and said, the tire was not replaced. I took a picture in the lot of the gauge and the guy that told me that the car was safe. I have had several communications with their management. will all my evidence to my horrible experience they wouldn't do anything. when you rent from this company you are powerless as they don't car and they know you can't do anything about it. I have never had a worse experience with a rental company!