It is unfortunate you have found yourself in this predicament. From the information you provided, you may have an issue in the lower end of the engine as was indicated by the above poster. If I were you I would take possession of your vehicle from the mechanic and find someone who can properly diagnose your lower end issue. The low oil light indicates oil starvation due to a worn oil pump and this is where the damage occurred to the lower end. The overheating issue is unrelated, so you have multiple issues going on.
As I see it you have a couple of options. If you own the car outright, you may consider trading it in and getting out of it completely. If this is not a viable option for you then I suggest you find a knowledgeable mechanic who can properly diagnose the engine noise. The older more experienced mechanics can do this. There are some who can tell a rod knock from a main bearing knock. That is who you need to find.
But lets say for discussion sake they determine you have either a rod or a main bearing issue that is causing the knock. At this juncture, I would be looking for a remanufactured short block and have it replaced outright. Of course if you're handy and want to take it on yourself, that would be my vote, but from your conversation, it looks like you would rather leave this type of effort to others (and theres nothing wrong with that).
So, to recap - find an experienced mechanic to properly diagnose your noise. Cost should be minimal to do this. If the noise is in the lower end of the engine (which I suspect given the information provided), you either offload the vehicle entirely and get into something else or bite the bullet and get a remanufactured short block. If you're going down this rabbit hole, you may as well price in a complete remanufactured engine just so you know where your financial limits are. Personally, I would stay away from any used engine replacements. It is a headache you do not want.
I feel for your situation and understand your frustration and wish you all the best!