I bought an expensive inverter, I cut the plug off to feed the cable throug a hole I drilled in the cupboard

I bought an expensive inverter, I cut the plug off to feed the cable throug a hole I drilled in the cupboard. I fitted a new plug, the unit did not work. I returned the unit to Takealot and Takealot rejected the return due to me putting on a new plug. I am a qualified electrician and Takealot blatantly just refuse the return due to their so called return policy. One can also not communicate on a personal level, just via e-mail and to very *********** people.