What’s wrong with my resistance calculations?
One mistake is to measure a device designed for 240v AC with a fraction of a volt DC. Another is to try to apply Ohm's Law in situations it's not meant to handle.

Low voltage

It's likely that your blender uses a brushed motor. The brush to commutator contact is notorious for being unreliable, at least at the low voltage and current a meter uses. An oxide film can build up, which is easily punched through by 240v, but can be very high resistance at volt and mA levels.

While measuring the resistance, turn the motor by hand. You may make better contact by moving the commutator under the brush. When you get to measure the real resistance of the motor, you'll find it's far, far lower than the 960 ohms you expect. 

Should Ohm's Law work here?

Ohm's Law is only useful when we're dealing with things like passive resistors, where the voltage across it is generated by the current flowing through it. The ratio of these two is relatively constant. It's affected slightly by temperature, strain, age, but otherwise fairly constant at the one or a few percent level.

In a blender motor, the terminal voltage is the sum of three main things. The first is indeed due to the resistance of the copper windings in the motor, probably less than 100 ohms, generating a small voltage due to the current flowing. The next is the inductance of the windings, as the current flowing is AC. The largest component is the voltage generated by motion of the motor, the back EMF it's generating, which of course depends on its speed.

You can take the ratio of voltage to current under some conditions of speed and motor loading, and call it an effective resistance (more strictly it's an impedance, but it still has dimensions ohms). Once you've done that, it's not actually useful, as that number can change by a factor of 10 or more between standstill and maximum speed.