Do not be too concerned as it is not that uncommon to see this sort of failure of proper response to down regulation treatment.  There are various options that may help to overcome this. You could try again with the same dose of Buserelin as cycles and hormone levels vary so it may work.  Buserelin is usually administered at a dose of 250µg or 500µg per day.  If the lower dose was used, the higher may work better. There is no evidence that alternative down regulation drugs would be more effective.  Another option is to try treatment without long down regulation.  IVF treatment using GnRH antagonist such as Cetrotide may overcome this failure.