As Paul has explained, it's archaic/obsolete. In the past, 'use' worked like any other modal verb, hence the form 'usen't'. It was just like 'wouldn't', 'couldn't', 'shouldn't, mustn't. For a while, 'use' was like 'need' and 'dare', with the alternative forms 'needn't' and 'daren't' and 'usen't', but the modal forms of 'use' have now disappeared. 'Usen't' doesn't sound wrong to me - simply very old-fashioned. It doesn't surprise me that many native speakers, especially younger ones, hadn't heard of it. If I were you I'd try to update your 1954 grammar book, though!

I've heard this used by native speakers in Ireland. Can you tell us if there was any context for the sentence, which grammar book it was or even where your book was published? Even if the form exists in a dialect of English, as a learner you must follow the standard grammar (didn't use to). If you drop "usedn't" into a sentence, we'll just think you've made a mistake.

I really am curious about the grammar book you have seen this in because no, it is not used. It is obsolete.I have never heard it used by anyone. You used to live in Leeds, didn't you?

I have never heard that in my entire life - not used here in the States, if it even exists.

You can't say usedn't. Here is how we would say these sentences. You used to live in Leeds, didn't you? She used to live in Manchester before she was married? Didn't she live in Manchester before she was married?