Engine not working

I love my 2005 Shinka, not sure why since it costs so much in maintenance, but here is the latest. The engine was replaced by the recall several years ago, by Mazda. It now has 63,000 miles on the new engine and Mazda says it is shot and needs replaced. WHY does the engine not last longer, but, the main issue is replacement. I owe 8,000 on the car, have no money, and now am told it will cost 7300 to replace the engine. Suggestions sorely needed. As a trade it they will give me 1000. help, in tears. wife of stinger