i advise you apply for reconsideration and explain every details on a cover letter. you have a very good chance for approval.
unfortunately, you are still liable to pay for reconsideration even though it was the HO mistake on the dates.

I have been a silent reader for several years and this forum has been a great help. in returning the favour I hope my story helps anyone waiting to apply for naturalisation. This is an advice regarding the 10 years good character rules. I read about how some people had been refused based on the new ...