I think it is worth trying.
There have been many instances where companies can come up with a more favourable outcome, and sometimes even do a complete u turn, once the FSO becomes involved.
Some examples of rectification or compensation provided through mediation:
The complainant’s insurance company voided a home insurance policy and refused a claim on the basis of non-disclosure. In Dispute Resolution the company accepted that this was an innocent non-disclosure and reinstated the policy and agreed to pay a percentage of the claim.
From page 8 of the FSO’s 2016 annual review here;
https://www.fspo.ie/documents/archives-fso/Financial-Services-Ombudsman-Review-2016.pdf