Council tax toilet paper lol

[Tevion]

I opened a letter which goes
DATE 9 Nov-2009


PERSONS JOINTLY AND SEVERELY LIABLE-
MR BRIAN BLA BLA
THEN MY ADDY
Dear/Sir Madam

North lanarkshire council
council tax 2006/7
We write to advise that the undernoted balance remains outstanding. You should make arrangements to settle same, with this office, without delay, if you wish to avoid further action being taken.

A STAMPED ADDRESSED ENVELOPE MUST BE ENCLOSED WITH ANY CORRESPONDANCE SENTTO THIS OFFICE IF A RECIEPT OR REPLY IS REQUIRED

Yours Faithfully
Charles Anderson
Balance outstanding £105.59


Right I am new to all this so why do they need me to provide them with a stamped addressed envelope and what should my next step be they have bought the debt from the council obviously but they havent stated a timescale to reply to this ie like a notice the letter I recieved is almost an exact replica of what I have wrote apart from account details ref number

Thanks fellow humans for any help