Pegasus App Charged Twice for Baggage Without Adding It

I booked two Pegasus Airlines tickets via Lastminute.com for the route Stuttgart – Istanbul Sabiha Gökcen – Stuttgart under the name Biljana Vojnovic, using the email address biljanavojn***@icloud.com. The outbound flight was on 4 May, flight PC970 from Stuttgart to Istanbul Sabiha Gökcen at 14:20–18:10, and the return flight was on 7 May, flight PC971 from Istanbul Sabiha Gökcen to Stuttgart at 14:55–16:55. During the booking process I was informed that I was only allowed to take a small cabin bag (40×30×15 cm) and that any additional luggage had to be booked and paid for separately. On 29 April I tried to add checked luggage for these flights via the Pegasus mobile app. I completed the process and a payment of 68€ was charged, but the additional baggage did not appear in my booking and the app showed an error message instead. Thinking this might have been a technical issue, I tried again on 30 April, this time paying 32€, and once again the booking did not show the added luggage and I received an error notification. Despite these error messages, both payments were successfully taken from my account. Later, when I did the online check-in, I was finally able to add the additional luggage successfully in a separate transaction. After that, I contacted Pegasus guest relations and requested a refund, but my refund request was rejected without any explanation or justification, even though the service was not added to my booking due to the app error. I kindly request a full refund of 100€ (68€ + 32€) for the two unsuccessful baggage purchases on 29 and 30 April, as the additional luggage was not provided for these payments and I had to pay again during online check-in for the legitimate baggage purchase. I also ask that Pegasus investigate and explain why the app produced repeated errors while still charging my card, and why my initial refund request was refused without a clear reason.