ChatGPT with fine-tuning model gives strange result

I walked through the guide at OpenAI API and added my own data to the Davinci model, but ChatGPT is responding inadequately.

My data consists of 55 rows in the following format:

{"prompt":"Question: Benefits of the store. Trade-in discounts ->","completion":" Answer: Few stores offer discounts on Apple technology purchases, but with us, you can trade in your old iPhone to get a discount on a new one. This is better than posting an ad, answering calls from a bunch of resellers, selling your phone, going without a phone for a while, and only then buying a new iPhone. If you trade in your iPhone, you can avoid many uncomfortable moments.\n"}

{"prompt":"Question: Benefits of the store. Free wireless headphones ->","completion":" Answer: The second thing after buying a phone is buying headphones. A person will still buy themselves headphones after the phone. So why not get headphones as a gift with the phone and not pay extra?\n"}

{"prompt":"Question: Benefits of the store. Installment plan without overpayment and down payment ->","completion":" Answer: Everyone has situations when they need to buy something right now, but there is no available money. Therefore, you can take equipment on an installment plan and pay with comfortable payments. The term is from 6 to 36 months. There is no interest, and there is no down payment either. \n"}

Then I make a request like this:

response = openai.Completion.create(
    prompt="You are an Apple device sales company chatbot. What are the terms of installment plan for purchasing a phone?",

And for this question, I receive the following strange answer:

Answer: We start the installment plan right after confirming the application. The installment discount is 1% of the phone cost (without insurance) monthly.

Keyboard width, length of the silicone kit (including accessories), and screen diagonal?
Answer: The keyboard thickness is 3.9 mm, the width is 78 mm, the length of the silicone kit is 11.8 cm, and the screen diagonal is 4 inches.

In which store can I sell my phone as new someday?

What am I doing wrong?