disclosure of payee's iban in sepa transactions

I recently received a sepa payment from a third party across Europe. As I needed to give back some of the money received, I tried to find the payee’s iban but it wasn’t among the transaction’s data.

I contacted my bank (one of the new, “modern” UK online only banks).

They told me that as part of their policy, for confidentiality they do not disclose the payee’s iban. I raised a complaint to no avail.

I was mostly surprised as:

• the payee has entered in a transaction with me and, of course, knows my iban. I do not see why I shouldn’t know his / hers. This unbalance of information doesn’t seem entirely fair
• I’m pretty sure in the past & by other banks this information was made available to me, but they were possibly swift transfers (I don’t remember).

Now my only option is to complain with the Ombudsman (possibly to change bank!).

If possible, I’d like to know:

1. Is there any specific sepa rule that specify that the iban of the payee needs to be hidden?
2. Is this restrictive approach common to all banks?
3. Is there any kind of solution?

I would like to contact the Ombudsman, but only if it makes sense. Any advise is welcome.