is there anything listed for your exchnage here http://usertools.plus.net/exchanges/mso.php
have you tried the obvious reset of the hub/router
if there is nothing suggesting any problems at the exhange that the links tell you in imjolly's post then:
1) are you connected by master or test socket?
2) Do you have any other telephone sockets?
3) Can you do a quite line test by dialling 17070 option 2. There should be no noise but slight hum normal on cordless phones.
4) can you please post your adsl line stats. Help shown below
5) can you run a full bt speedtest by going to http://speedtester.bt.com (not beta version)
ADSL Line Stats Help
If you have a BT Home Hub like the one below...
2) click Settings
3) Click Advanced Settings
4) Click Broadband
5) Click Connection or sometimes called ADSL (see picture Below)
The direct Address is http://bthomehub.home/index.cgi?active_page=9116 (for bthomehub3)
Please copy and past the adsl statistics and post them here (you may get a error but pressing POST several times usually works)
The exchange migration (for ADSL2+ BTw's 21cn network) involves lines being manually transfered to the new 21cn network in batches. The adsl2+ service will allow speeds of upto 20mb compared to the old adslmax which was upto 8mb.
This process can take days/weeks/months after the exchange is 21cn enabled.
first time on the forum that the upgrade to 21CN has taken 3 days normally 10min disconnection an then on to 21CN
it can take days/weeks/months after you receive the email before your line is upgraded but during the wait your connection is ok just still on adlsmax - not lost altogether
Its Openreach that do the changeovers in the exchange. Unless they provide a status update to BT retail, then the situation is unknown.
Its possible there has been some equipment problems after migrating the lines. It would not be easy to move them back onto the old equipment, so its probably in the hands of BT Wholesale, to sort out the faulty equipment or configuration.