When I became a customer of UB in 1978, the customer service was fantastic at Branch level. There was never any need to go further. If the local manager turned you down, then you were rightfully turned down.
Sadly, over the past 40 years, they moved from Bankers to Sellers of Money and there...
In Ireland, insurer must issue cheque within 10 days of the settlement being agreed. You too have 10 days in which to consider the adequacy of the offer.
If you are waiting a month,m I'd suggest you write to your solicitor asking for the identity of the insurer and their reference number...
You are unfortunate in that you seem to have a couple of what you call errors, but which Revenue might call fraud(??) You could certainly have a full audit so as others have suggested, the Voluntary Disclosure is the only way to go.
Although technically not the correct etiquette I would ring the insurer directly and ask to know precisely what sum was transferred to my solicitor.
Insurer will NOT discuss anything with you, if you have a solicitor involved. They will only discuss with solicitor.
Tis important to read your Policy as Leo states. Some insurers only allow a total of as little as 90 days vacancy in any one period of insurance, whereas others might allow up to 60 days continuous vacancy.
Perhaps you could consider moving the GBP to an account in Ulster NI?? Then use a GB based stockbroker. You can find some with low commissions, but you will find it difficult to find someone to deal with in certificated form. They all tend to use nominee a/c.