Hi FL & dx
Now I have had more time to think about it
I agree with dx100 at this stage and you should just ignore the first letter and wait so they know you are not interested.
However, in view of your previous correspondence it will probably be a good idea to send a letter in the future to explain why you are not prepared to deal with them.
I think they will then go away for good as they can't send it back to HSBC.
Keep me informed when the letters arrive.
Regards
Pedross