Iphone Sim Unlock

Hi All . My Daughter bought an iphone 15 PAYG intending to use a different providors sim . Unfortunately she has now discovered its sim locked . Three will unlock it once she has purchased enough credit but she doesnt want to stay with three . I have read there are plenty of scam unlock sites , or sites which offer phone unlock services costing q bomb . Could any savvy member point me in the direction of a reputable and reasonable unlock service . TIA