Here are your parts



On the belt size I went to the Whirlpool site and got what they showed for a belt and then cross-referenced those numbers back to AppliancePartsPros and the belt you received is the correct number. So I do not know what is happening there.
Note: I do not work for AppliancePartsPros so I would give them a call.

I did find the install sheet that should have come with the belt and it does say it will be different, see attachment.

Try turning the drum by hand. Should turn fairly easily. If not could be the drum is jammed for some reason. You may want to try this on a couple other dryers to get a feel for it.
If it is difficult to turn run your fingers around the back and front of the tub to machine seal. To see if something has jammed between the tub and frame (bra wires are famous for this). Be careful in case the object is something sharp.
If nothing is jammed in there you will have to open it up and find the cause.
Check the rear support wheels, the front support, the idler wheel and that the drum seals are not folded under.

If all are OK then odds are that your motor is on it's last legs.

Note: If you have heat when the motor will not start there is a problem with the centrifugal switches on the motor. Could be they are activated when the motor is at rest so the start winding in the motor is not in circuit and therefore will not start.