If it is safe to put some heat on the nut ,that might help you to loosen the bolt
Pour boiling water on it from a kettle. Or warm it up with a portable blowlamp. Heat usually works. If the hexagon is buggered you will gave to use Stillsons or similar.
WD-40 does not dissolve rust. Whip up your own rust solvent with a 50/50 mixture if acetone and automatic transmission fluid.
"I have tried all my tools which is ruining the bolt's shape"
Then it is time you got some tools that fitted properly. You need an all wall drive socket the correct size exactly before you do any more harm. Halfrauds sell them singly so they cost is not OTT.
time to get out the cutting wheel/ grinder.
The bolt is very tight and I have tried all my tools which is ruining the bolt's shape. I sprayed WD40 but that didn't work. What I can do to loosen it?
