Unfair default??? Advice needed

Jsn07

I hope I am putting this in the right place as I need some advice. I took out a QQ loan 15/08 and on 15/09 I requested it be extended and paid the intrest up to that date. The next payment was due 15/10 however due to personal reasons I had to take unpaid time off work therefore could not make the payment. I got a missed payment email and letter so called them to explain and basically was told to call back when I could pay and not to keep calling for every letter as the send lots, in fact I only got 2 letters but got a email every week. Anyway I made the payment 15/12 in full so it was 2 months late. At no point was a default mentioned yet one was put on my credit report and as they didn't tell me I only just found out. I contacted QQ and asked why I knew nothing about this. They said they sent a notice of arrears 20/09 that said I had 15 days or it may be reported to credit reference agencies. I have asked if this was the case why was I not told post/email or over the phone. Why is the default dated 15/12 the date I paid and not November if that's when they said the 15 days were up? I'm finding it hard to see how this is fair? I know I missed the payment and that's my responsibility and if I could have paid I would have so please don't comment it's my own fault I know that and pointing it out won't help. But how can a default be fair??