The customer can ask their bank anything, but the SEPA terms allow reversal for very strict scenarios, only if the payment was erroneous, it was duplicated by a human or technical errors, the wrong amount was sent etc. So the bank will refuse demands based on consumer protection reasons, they correctly fulfilled the customer request to send the money and further disputes are handled privately.

You might be referring to SEPA direct debit, which can be reversed unilaterally by the client at any point during the 8 weeks. These are payments initiated by the merchant, using an already established direct debit channel.