A : I didn't like it. B : I didn't USE to like it. "A" refers to a single event or occurrence in the past that I did not like. "B" means I did not like it in all the past before now, which may have included hundreds of events or occurrences. However, NOW I DO like it. (something changed my attitude or opinion or liking of it)

In what way do you use "didn't" and "didn't used to" differently? For example A : I didn't like it. B : I didn't used to like it. I didn't use to like it. ( I did not like it before but I like it now) Grammatically not correct. Sometimes this is used in speech but not often in writing.

I didn't like it. = 好きじゃなかった。 I didn't USE* to like it.= 好きだったものじゃない。 As corrected it should be "use", not "used". And that's a sentence you'd probably never hear, in Japanese too I think.