But isn't the issue here the fact that your matter was not handled correctly after service of a valid notice, I.e no follow up and the notice expiring, thus resulting in a new application and service of a new s.42 notice at greater cost.
This is not an issue about service of the initial notice but failings thereafter. Was there no mention of that in your complaint and the ombudsman's report?
Do you have any further questions or queries? I am happy to assist further.