Replaced battery starter

Two months ago I replaced the battery, have drove the car and then it woulndt start cold silence. Checked battery, alternator and starter, starter was burnt out got new one and it cranked but wouldn't stay on got the car off the lift to crank it wouldn't went to dead silence again disconnected battery again it started then few hours later tried to go to work and it clicked then went back to dead silence tried to start it for almost a hour still wouldn't start. Thirty min later it started up then got it to my friends to help me figure out what was going on again we retested the battery its reading correctly, he checked fuses inside and out we made sure all grounds to the starter were good and checked th ones to the car everything was fine we tried starting it again watched the starter burn up with smoke. Haven't took it back to get another Because there is only one left before I'd have to wait to order one. What could be our problem it's not my fly wheel either we did spin it and the old starter woulndt spin so now I have two starter that burnt up and the smell of the new one I have noticed I been smelling that for a few months so it's been burning up we are lost on what the problem could be because we have checked all wiring fuses ect and still no clue