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 idk 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 idk if that is the cause or what

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