Thanks a lot I willl do that:)

Hi everyone, I'm new to this site, but just want to say thanks to everyone who posts on here, as it has helped me immensely so far! I have started a claim against Natwest for £1585 (no interest) They have replied to my preliminary letter asking for the money back with an abrupt 'no', 'but thanks for taking the time to write!' I am about to send the letter before action, threatenning to take them to court, but I'm unsure which address I should use to send it to. I sent the initial letter asking for the sum to my local branch, but had a reply from the Customer Lending Centre. Which address should I send the next letter to, my local branch, the cutomer lending centre, or the registered head office address? Don't want any unecessary delays, this whole process of taking Natwest to court is making me very nervous anyway, I just want to get on with it!Can anyone help?