[ADVICE] Client asked for revisions that is beyond my gig's scope. What do I do?

A client (who has become a regular) had asked me to do sing a song in my gig. Upon delivering the song, they started asking for revisions which is beyond the scope (such as copying other people's style which I cannot do since replicating other people is hard in my niche). I explained it to them yet no response. I'm considering to cancel the order but I'm afraid it'll hurt my metric (even though I have 100+ orders already). Any advice is appreciated thank you!