TAP Air Portugal changing flight for free is not possible [closed]

I booked a flight from Vienna to Lisbon on the 2nd of July, with flight date of 7th of September. It is a Classic ticket, so basically it permits flight changes with a fee: (75€) + difference.

However in July TAP started a new campaign, as the first change is free for everyone: https://www.flytap.com/en-hu/promo/book-with-confidence now they extended this campaign until 31st of August. This was the reason why I bought my ticket, but now things happened and I need to change my flight date from 07th to 17th of September.

Prices are the same, so I think it should be free to change, but their system says I need to pay 75€. I read all their conditions and I am 100%s sure that I should be eligible for a free change. Also tried to connect customer support in messenger, telephone, even I filled a complaint on their website, but haven't received any answer after 2weeks of waiting. Obviously I don't want to pay 75€ (from this money I could even buy a new ticket), but I don't know what else options do I have. Cancellation is not possible, I mean I would not get any compensation. (I hope they will cancel it and then I could get a voucher at least.) What should I do in this situation? Also, I don't understand why are they advertising things which are not true?

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Can you change flight days for free?

Any change made to a flight once it's booked by a passenger is known as a schedule change. Flyers can use a schedule change to their advantage to change their flight for free or even request a refund.

Can you change flights free of charge?

Some airlines allow you to change your flight within 24 hours of booking for free. How should you change your flight if this is the case? The best way is to call customer service. That way, you can confirm your airline's policy and make sure you won't be charged any fees.

How close to a flight can you reschedule?

Yes. You can change or cancel your flight up until 10 minutes before your scheduled departure time. For example, if you had a flight scheduled to depart at 8 a.m., you'd have until 7:50 a.m. to make changes or cancel the flight.

What happens if you need to reschedule flight?

Unfortunately, in most cases if you need to change a nonrefundable ticket, you will be subject to a hefty change fee. The change fee varies by airline; most major carriers charge $100, depending on the airline and the exact restrictions of your ticket.

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