Your priority is to sort out your finances and to reach an agreement with Ulster Bank.
You are not happy with the person you have dealt with and you have a complaint to make. Write a polite letter setting out your issues and return the documentation which was sent to you in error. Not a copy, but the original.
Mistakes like this get made. Ulster Bank needs to investigate it.
They should appoint someone seniior to deal with you.
In my experience, the banks generally have been very helpful to cusomers who cooperate with them and Ulster Bank has been particularly flexible. You have already reported on your good experience with them in
this post.
As with any organisation, you seem to have got off on the wrong track with the wrong person. Complain and they will send someone else to deal with you.
If you are reasonable, they will be reasonable.
Forget about the Data Protection Commissioner. This is a once off error which happens in all organisations.
Brendan