I wonder if you "owe" someone for "NOT" performing the "service" you "hired" them to do.
Is there another groomer you could use? If so, you might talk to a new groomer, explain the problem you are having with the current groomer (repeatedly cutting hair you said NOT to cut) and see how they react.
If you switch groomers, you also might even let the current groomer know they are losing a customer BECAUSE they refuse to allow the topknot to grow out, as requested by the pet owner, and cut it off WITHOUT your permission.
Another thing you could try is to take a band and bow...go to the 'dollar' store and get a cheap but cute clip in maybe...even Kmart had some cute, inexpensive infant hair bows in their "baby" section...something you won't care about if lost, or a tiny scrunchie...the Family Dollar I went to a few months ago had bags of 300 for $1-$2, etc...
WHEN you take your baby back to the groomer next time, and say that
the topknot is to be grown out and
ask the groomer to put the hair ornament(s) in to hold the hair up after the grooming is complete.
With physical 'evidence' in hand, perhaps she won't
forget.
I am sorry you are having this trouble. I like the topknot up...hate the 'visor' / 'bangs' hanging down into the eyes...but worse, it is awful when people 'ignore' you, especially when you are paying for their services.