Your diagnosis is in right direction. IT is delusion of persecution. However delusion of persecution is one of the symptoms of schizophrenia if other symptoms present. Or it may be diagnosis of delusional disorder type persecutory. If it is delusional disorder , difficult to cure almost 10 to 20 % cure rate. However it can be controlled very well with medicines.If medicines stopped, recurrence is there. If diagnosis is schizophrenia, probably life long medicines needed to keep pathology under control.Continue one doctor if possible and whichever the medicines effective continue them for long time without changes.