Before you call anyone about a disposal, there are two things worth trying — and one of them often sorts it.
Try this first
If it hums but will not turn, the motor is fine and something is jammed. Switch the power off at the wall, use the little hex key that came with the unit to free the flywheel underneath, then press the reset button on the bottom. If it is completely silent, the reset on its own often does it. We would rather tell you this than charge you to come and press a button.
When it really has finished
Water coming from the body of the unit rather than the connections means it has rusted through and cannot be repaired. If it keeps tripping after a reset, the motor is going.
Older kitchens and older drains
Fitting a disposal to an old cast iron drain sometimes uncovers the real issue — a line already narrowed with buildup that cannot take the extra load. If a new unit causes immediate backups, the drain is the problem rather than the disposal.
What it does not deal with
Cooking oil and fat. Those go down warm and set further along the pipe, and that is the usual reason a kitchen drain keeps blocking.