Such poor QoS is either due to :
1/ a terrible error in your frequency planning (same freq + same BSIC ?) (same frequency within the same BTS ?)
–> in this case, call drop, cssr and voice quality must be very bad too…?
2/ a software bug.
Now I am not familiar with nokia, so I cant tell you how to fix a sw bug. But you could try deleting the BTS from the OMCR and re-create it from scratch. That might clean the system.