Name change and possible fraud - UK - BE National

Hello reddit,

Please don't be too rude, I know I have made mistakes, but I didn't know half of what I was getting into and I own up to that resposibility.

I think I might have majorly fucked up by accident. Just over a year ago, I got enganged to a British national and moved a couple of months later to live with him. Here, it got difficult to get a job, because my name is very... special. People can't write, spell or pronounce it, and it was holing me down on the job market.

We looked into it and decided I should change my name per deed poll, into something british. I was getting married anyway, and my fiance also wanted to change his last name, and if that could be done by taking my changed name upon marriage, that's even better. We even called the embassy AND TOLD THEM about the name change, but mentioned we were getting married and I would apply for dual citizenship. They said (to my fiance, i have extreme social anxiety and am literally unable to call people) my deed poll would be recognised. I wrongfully assumed this meant: it is accepted all the way. Today I found out this is wrong. My name change would only have been recognised upon obtaining the citizenship and me and my fiance split up months ago. I am about to move back to the United Kingdom (Northern Ireland), and have been made a job offer in my new name which I signed in that name as I was, also wrongfully, under the assumption a deed poll is binding and using my old name was considered fraud. So I actually have signed official documents (ex. employment contract) with my new name, which isn't and won't be recognised. I have no idea how illegal this is but I've been having panic attacks for hours now. I have informed my new work of my name change, explaining i understood it wrong and I won't be able to apply for my name change and have requested to use my old name on all the documents. Is this illegal? Deed polls are recognised by a lot of goverments, and thanks to me misunderstanding the embassy I was under the assumption it would all go through, and I have no idea what to do now.

I am so sorry if you think I'm a stupid idiot, because believe me I do as well.

TL;DR: assumed my name change per deed poll would go through after confirmation by the embassy, turned out they meant after i had gained dual citizenship, which i won't gain any time soon. I have, in the past, signed legal documents with my new name, which is not recognised. How illegal was that? In how much trouble am I?