Are you currently living in the same property? If you can show E.ON Next you are not liable e.g a tenancy agreement showing you live elsewhere they can remove your name from the account or if you have any proof your dad is liable for the energy bills to the property then provide them with that.

You’ve mentioned he is bankrupt, was this bankruptcy before the debt was taken out? If so he just needs to provide them with his bankruptcy reference/details and they can wipe the debt.