2011 Mitsubishi Lancer electronics problem

My partner had overloaded her car with oil and had to get road side assistance to get it towed to a garage after smoke was pouring out the car on the motor way. The roadside assistance guy checked it and said she was lucky not to blow the engine on the car but would need a full clean out of the oil and filters. A separate garage that my partner took the car to done an oil and filter change, changed the starter motor (I believe) and replaced the battery as he said it was flat. Now we are worried about the integrity and honesty of this guy because he’s refused to give a breakdown of what’s been done or a full receipt of cash we have given him for the work being done as his card facilities at the garage were “not working” now all of a sudden there is something wrong with the cars electronics now and he’s sent the car down the road to a friends garage as he said he doesn’t knows anything about the electronics of a Mitsubishi Lancer. Now this new guy (electronics engineer) Has the car and after inspecting it, its an old battery that’s flat in the car (after the other garage charging us 120 pounds for a new one) and the starter motor is a refurbished one, not a new one, he’s saying it may cost thousands to replace the electronics under the dash. I’m wondering if this simple job has turned into a nightmare because they guy has seen a female coming and thought sucker! Does anyone know anything about Lancers and is this something that’s expected to go wrong with something like this and the electronics of this car?

There is nothing special about the lancer and no this does not happen as a regular problem with any brand.
You need to just have it towed to a real shop and I don’t think there is a regular member here from the UK ( I guess that is where you are ) . As this is mostly a USA based forum legal advice can’t be given .

Overfilled oil won’t require a flush, nor will it damage a starter nor will it kill a battery, nor will it hurt the electronics. These guys are shysters and they are scamming the holy heck out of you. Tow your car away from these people as fast as you can.