My vehicle came out of the shop with a new issue after replacing the head gasket?

My 2000 Honda Accord LX was originally overheating so I figured the thermostat was bad. I planned on replacing it soon, however I wanted to replace the spark plugs before I did that. The vehicle had obviously overheated a lot before I bought it because the spark plug wires were melted to the engine. By the time I got all the spark plugs out one spark plugs threads ripped out of the engine. I brought it to the mechanic to fix it, and they found a lot of radiator fluid in the cyclinder. So they had to replace the head gasket and replaced the thermostat as well. However when I picked the vehicle up the vehicle was limiting at 3000RPM it was in limp mode. I brought it back and they ran a test and said the code called for a replacement of the alternator I opted to replace it myself but it still didn't fix it I brought back and they said I'd have to replace the ECU I didn't wanna spend 300 dollars on something that might not fix it. The current code I'm getting is for the Cylinder Position sensor (not a crankshaft position sensor) which is in the distributor housing so I replaced that and still didn't fix it it's been almost a year since I brought it to the mech i don't know if I can threaten a lawsuit to have them fix it since that problem wasn't there when I gave it to them or if anyone knows how to fix it also they said that my knock sensor was out so they put it back in i don't know if that is the cause or what

Your problem is trying to diagnose and work on it yourself. The shop is simply going to say it's an issue with you driving the overheating car, or the work you did on it, and wash their hands of it.

They are also probably correct in this. If the engine got hot enough to melt the plug leads, who knows what other damage was done. Sorry but you bought most of this misfortune on yourself by continuing to drive an overheating engine.

Don't waste your money seeing them. A 15 year old car breaks down. Regularly. They didn't break it. It's just old.

I did not continue to drive it while it was overheating I bought the car 2 days later it started overheating I stopped driving it and ordered the thermostat while I was waiting for it to arrive I replaced the spark plugs and discovered the issue. There's no way the car suddenly has this issue of being in limp mode for no reason I'm thinking the timing belt is off just slightly