How Stupid is T-Mobile?

On Thursday I got a letter from T-mobile, complaining about my mobile interenet usage in December:

Basically, in December, I used 7.7Gb of data, rather than the fair use amount of 3Gb.

Should you continue to use more than your fair use amount between 1st January 2009 and 31st January 2009 we will have to reduce your connection speed to 64Kbps...

Whilst T-Mobile are perfectly within their rights, it would probably be in their interests to try and improve their customer service attitude:

1) A look at my data usage over the previous 17 months of the contract would have shown the high usage to be anomally (due to moving house) rather than the norm, and as I regularly have a £100 of my monthly call and text allowance left over you'd think they would be a bit more leniant.

2) If I had continued to use data at the December rate, then telling me on January 22nd would have been too late to prevent me going over their limit in January; thus forcing me to be reduced to 64Kbps.

...and most importantly:
3) My 18 month phone contract ends this week. This letter doesn't persuade me to sign-up with T-mobile for another contract.