Are the water and electricity that were used without registering the account in the tenant's name considered usurped, and does this entail sin, and is it obligatory to compensate the company for the difference in consumption?

The tenant must pay the full cost of their electricity consumption to the company, because it is not permissible for them to use deceit to benefit from the landlord's discounts. Your father must seek forgiveness from the company or fulfill its right. Nothing of the aforementioned is binding on the questioner, and they should disregard these whisperings (waswas).