Change the narrative style by using indirect speeches :

"Have you killed the rats?" said the Mayor. "Yes, I have," replied the piper. "Give me the promised money." "How funny you are!" said the Mayor. "Take only fifty." "I was supposed to be given fifty thousand guilders," said the piper. "What have you done? The work you have done is very simple," said the Mayor.

The Mayor asked the piper if he (p) had killed the rats. The piper replied in the affirmative that he (p) had killed the rats. He (p) then requested/told the Mayor to give him (p) the promised money. The Mayor exclaimed with wonder that he (p) was very funny and told/ordered the piper to take only fifty. The piper said that he was supposed to be given fifty thousand guilders. The Mayor then asked the Piper about what he had done and added that the work he had done was very simple.