From your description, your single transistor is in common emitter configuration. It inverts signal polarity. You must send it through a second transistor, to deliver the proper signal to your servo.
There is a chance that one transistor can be sufficient, if you can make it work in common collector configuration. However the output voltage may be dropped by 0.6V. Then it is 4.3V and it may not be recognized by the servo.
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Or, simply cause your pic to deliver an inverted signal. Then a single transistor is fine in common emitter configuration.