To be fair to the OP, it's not really a matter of 'dodging', since no-one has actually asked the question!The question you seem to be dodging is, who the F installed it for you?
It rather sounds as if whoever did it has really only done the plumbing (quite probably satisfactorily) and attached the new shower to an existing cable - in which case there may well not be anything that really warrants being refunded. It sounds as if the problem, electrically, is more a matter of what was not done (and, one imagines/hopes, was not charged for!), rather than anything which has been done....If it was a "pro" you need to get a refund ....
Kind Regards, John.