Unresponsiveness of Customer Service in Turkish Airlines

I purchased a round-trip ticket from Berlin to Istanbul. There were no issues when flying from Berlin, but when I tried to do online check-in in Turkey, the website kept giving errors.

When I called customer service, they said that we had entered our information incorrectly while purchasing the ticket, which resulted in an extra charge, and they took ₺7,000 from me. Later, when I called customer service again, they told me that they had suspended online operations due to high volume and that any actions taken through customer service would incur a fee.

I stated that the charge was unreasonable and that I had invoices to prove it. They created a complaint form and told me I would be contacted as soon as possible. It's been a week, and no one has called. I do not accept this terrible mistake from such a well-established company.