Unknown CCJ

[sj_mith]

I never had a default in last 17 years and thus was the first and last default I hope. So the story goes as, I broke up with this girlfriend of mine and noticed after few months that there's a direct debit of £15 with Vodafone (my personal contract was with O2) in my account which I was completely unaware of for months (my ex knew all my details, I thought I could trust her). I immediately cancelled the DD. The DD was cancelled in March 2014. I moved to a different address following month and moved again in May 2018. In November 2018 I received a letter (first letter in all those years) at my new address from the debt collection agency demanding £275 for a ccj for their client Vodafone. Being a naive and not having a default ever I paid the outstanding amount immediately without thinking (I felt very guilty and ashamed Tbh). Now, I am planning to apply for a mortgage soon and this CCJ is bugging me as it has ruined my credit score. I know that the judge can argue that I didn't act promptly but can I still apply for it to be set aside? Recently, I tried to contact the debt collection agency and to explain but they were quite rude. What is the likelyhood of a positive outcome? Is it really worth it? How long would it take to get the judgment?