New question on claiming back unfair charges, please help.

I sent my 1st letter to natwest claming back my bank charges last monday, today i rfeceived a letter saying they will reply in 7 days with a full responce or an update or progress. Now knowing natwest they will drag it on and on so what can i do to speed things up, or should i stick to my 14 day deadline as set out in the nitial letter i sent 9 days ago then send letter 2 as planned, please help.

thanks