Hy Suraj143,
With your circuit you will be asking the 555 to deliver 12A/8 Ohms= 1.5A. This will either blow the output stage of the 555, which can only supply 200mA, or overheat the 555 and destroy it.
You have two choices.
(1) Put a 56 Ohm resistor in series with the transformer which will generate around 320 mW.
(2) Design a different circuit which can drive the transformer at 12V.
It would be better in any event to drop the 555 supply voltage to 5V.
You will also need a couple of catching diodes on the output.
spec