Agreed services not provided and taken money then humiliating

Hello Sir/madam, I have given my study assignment to the agency where contacted the person she representing that it's her agency and also in the website the same number is getting floated. She had taken and promised to give quality materials but has given poor material because of that I have been failed in two modules for which I have paid money. She had told earlier as many times required by professor we will make the changes and give it to you. But everytime she's harrasing for money despite of taking agreed money in advance full payment. And in the last moment of submission she is playing every time. She is really doing fraud and torturing. Could you please provide any solution what should I do? Because of this I'm in huge pressure and went into hypertension. I hope to hear from you soon. Regards