Utility provider sharing personal data

Hypothetical scenario:

• you are with a utility provider for several years and paying by direct debit and e-billing.
• the utility provider sends letters containing your personal data (name, address, date of birth, bank account details etc) to the wrong address, several dozen times, over a prolonged period of time, without telling you.
• the recipient of these letters eventually rings the utility provider and tells them the intended recipient doesn’t live here.
• the utility provider doesn’t inform you of this having occurred, but updates its internal systems, resulting in your direct debit being cancelled unbeknownst to you, and the utility provider trying to charge you penalties for late payment of your bill.
• utility provider is satisfied that your personal data has not been shared on the basis that the recipient of the letters received over the years confirms over the phone that he never opened them.

Any thoughts on how one might address this with the utility provider?

Thank you.