Razmatazz, unfortunately you find yourself in a situation that would require the case officer to have some common sense and desire to help; something which she is clearly lacking. Unfortunately to her you are a customer to generate income - she does not care about the effect on your family or your neighbours at all. There is no reason at all why the works cannot be left in their current state on the condition that failing consultation meant demolition. If you are within PD rules for the elements that are built then simple reclassify them as outbuildings/garden structures. You are entitled to build a folly in your garden if it remains within PD. Have you considered discussing your issues with a local newspaper columnist? Every regional paper has one or two who write about local stories like this and, having worked in local government for some years myself, those columns do get discussed at senior management meetings and officers can get pulled up to explain them. The best ones make it onto staff noticeboards.
[little side rant...]
There are two types of officer in every town hall in the country. There are the ones who, on receipt of a forwarded email from months ago that was not acted on for any reason (even customer error) would move hell and earth to get the request/notification dealt with as quickly as possible, even extending outside of their remit and working unpaid overtime to do so. Then there are the jobsworths like your case officer who get a kick out of wielding their little slice of power. Unfortunately the public they work to serve -- sorry, customers they work to charge -- are just not important. Something about LA employment seems to attract those people like flies. Don't despair completely though, the current climate of cuts is weeding out those and leaving the better officers behind to pick up the pieces - because they are the only ones capable enough to do so. [sorry.... my little rant is over with. Having to put up with these people every day wears you down after a while.]
As mentioned you may want to consider writing to the information compliance officer at the local authority. If you want to then make an FOI request instead asking what happened to the email sent to xxx on yyy by zzz and, if reasonable costs allow, when and by who it has since been accessed. They have a legal obligation to answer you. (Ensure you keep the part about 'if reasonable costs allow' else they could just deny the entire request on cost grounds if they don't want to provide it to keep face.)
The rules for serving documents via the postal system are clear - you only need proof that the documents were posted, plus six days for first class and (I think) 10 days for second class. You do not need proof that the documents were delivered. If that is good enough for a court to base a judgement on then it is good enough for a local authority planning department even though some may consider themselves above the law.
There is some new information in your most recent reply. Are you claiming to have already reapplied for the neighbour consultation and it had run it course with an actual consultation having taken place? i.e. your neighbours received notification via the local authority?
At the end of the day take the planners out of it completely. With any development there are only two parties who are actual stakeholders - you and your affected neighbours. You are clearly coming towards the end of your patience and you claim that your neighbours are fed up with it too. Your wellbeing, and that of your neighbours should be a greater concern than your planning situation so you need to set yourself a cut off. One week, one month, or whatever your limit is. Once you reach that if you are still no further towards resolving this then cut your losses and demolish for your own health. Seek legal advice regarding your architect's incredibly bad advice that you were able to start building with the aim of recovering your costs. Don't get your hopes up as you are partly responsible, but professional negligence is insurable so it is worth pursing. (Check any bank accounts, mortgages, credit cards and car insurance products you have for legal cover - many have it bundled and they may be able to assist you.)