I have a Mahindra, too, but an older model. It doesn't really matter, because what I'm about to say will be so simple a child could do it.
Get you a pushbutton, normally open, switch and enough lamp cord to reach from the battery terminal of the starter to your seat, so you can operate it from there. Your local hardware store or building supply store should have these. A doorbell switch is fine. Connect the switch between the two wires on one end. Strip one wire at the other end, loosen the battery terminal nut of the starter, and put this wire under it. Tighten the nut. Strip the end of the other wire and connect it similarly to the switch terminal of the starter. That's the little terminal.
If you have a separate starter relay like the big ones they used to put on automobiles, your switch wire may go to that instead. If so, connect this last wire there.
Now, you have bypassed the ignition switch and ALL safety switches, so make doggone SURE you are in neutral before you push the button! If it starts and runs, you can leave this in place until you are ready to troubleshoot the problem. Just ALWAYS make sure you are in neutral before you push the button! My dad got run over by his tractor for standing beside it and THINKING it was in neutral. He lived.
If you want to get fancy and leave this in place long term, you might want to buy appropriately sized wire terminals for the starter end of this cable and mount the switch. It's your choice.
If it doesn't start like this, loosen and re-tighten your ground connection to the block and at least one of your starter bolts. You've already cleaned your battery clamps when you changed batteries. If it still doesn't start, push and hold the button, and have someone tap the starter solenoid or relay or both with a small ball pein hammer. If you can't get a hammer in there to it, put an extension or drift pin or something similar against it and tap on that. Something may be stuck or dragging inside the solenoid or starter or in the relay.