Seized motor

At this pointHi my car quit running on the interstate 2 days ago. I had it towed to a shop who had just replaced the timing belt and water pump about 45 days ago. They tell me when it has been looked at that the oil fiter came loose and that the motor has to be replaced. They also said it would cost about 5k. I asked them how this could happen jut being in there shop and they said. They never checked the filter because there was no need. Thet advised me to go to the place that did. My last oil change. I am a single mom with no money. Prior to being in there shop I had to use my tax return to put in a new transmission and clutch about 4 months ago 2200. I asked the shop if the previous repairs couldhve caused it but the say no. I also had one other shop look at the car before the timing belt and water pump was replaced but they only gave me an estimate saying I needed to replace the valves in the car so I got a second opinion because I couldn't afford to do that. So the car is now at the shop like I said who did the timing belt. They say none of the previous rpairs could have done this and insist I talk with superlube. My question is are they correct? I can't see how it can be in 3 different shops within 4 monthss and no one catch such a stupid thing that can cause thousands in repairs. I did however contact superlube and they said because they dot have record of my last oil change which would have been about 5k miles ago they probably aren't going to help. I will lose my car if they don't because I can't afford the repairs. They said the oil change was outside of warranty although mitsubishi reccomens every 7500 miles for an oil change. I had been going every 3 to 4 but with the car in the shop soo much I didt have the funds. Any advice you could give would be much apprechiated. One last thing I have a friend who says they might be able to unsieze the engine and I am wondering. Why the shop did not tell me this was a possibility. Thank you so much for your help.