Degraded ADSL line

After waiting for an age for someone at Tech Support to pick up the phone only to be told to phone Sales (about my Tech Query) I have now listened to music for more than 30min on 10213 and cannot take it anymore! After several years of a reasonably stable ADSL line speed of 5-6 Mbps since December I am now being told that I need to downgrade to a 2 Mbps line and even then it is dropping intermittently!?!? Surely Service should be improving not degrading? No-one can explain to me why this happens and if it is temporary?