How long ago did you send your first letter Rocket Dog?

As virtualtroy said their first correspondence is usually just a copy and paste job letting you know they have received your complaint.
If no follow up is received within four weeks I would be back in touch with them again.
I always use the online follow up form with my enquiry reference number. Making sure I am logged in to my BAEC account when sending any follow up information. (Assuming you are a member).