Well that didn't go well.
Seems like a reasonable response but I have a feeling my line is capable of more...
Yea you can see where he is coming from. They must get loads of people who give them the "my line use to get much more speed than its getting now" bullshine to try and get more speed.
However in your case it is not bullshine. If it were me i would send a polite email back just to reinforce the fact that you know your line is capable of getting a better speed and you believe the profile is wrong and was a manual intervention to fix it. (more on this below)
Forgive me if this is wrong but it might be of some use to you... once on an ADSL line we also had a lowered profile after bad weather and after a number of weeks the profile did not increase. After many weeks of complaining and not dropping the issue with BT, they had an engineer manually adjust the profile and called the service "manual intervention" or something like that. It was back to normal ever since. Now i am not sure if this can be done with FTTC but surely they can just bring your profile up and if the errors start happening again then the worst it will do is just lower again?
Hope you get this fixed in any case!
J