If you have as much luck as I did with them when I wrote a letter of complaint then I wouldn't bother.
The letter was sent in February, with proof of delivery etc, and I still haven't received any kind of formal written reply from them. How many months on are we now ?????
Make sure you take account of all names to whom you spoke !! Keep a record of when, and what you said.
Expect the billing to be messed up as well, then you won't be surprised when it is
If you want to write, I did actually get more luck with another letter when a manager in the customer services told me to fax to them direct and she would answer herself. From my experience, which hasn't been that good, I would find a nice CS manager.
Good luck !!