your explanation is not complete : how do you know you locked sector 3 instead of sector 1 ? by trying to make a call setup on sector 3 ?
actually, depending on your problem, there are 2 solutions :
1- TRXs of sector 3 are transmitting on antenna of sector 1, and vice versa.
2- the SUM card doesn’t recognize the TRXs that belong to their supposed sectors. TRX of 1 are recognized as TRX of 3… Check the SUM settings (i forgot how it is supposed to work)