What refund am I entitled to from BA if I first accept a change of itinerary

I paid EUR 670 for flights in August (VIE-LHR). First the outbound flight was cancelled, so I rebooked it (at no cost) for the next day. Now all the flights have been cancelled and I want a cash refund, but BA are only offering me EUR 393 (through their website). I assume they want to refund only the cheaper ticket I rebooked for the outward leg (plus the original return leg) – but I've still spent EUR 670 and they've cancelled my flights, so am I entitled to the full amount, and how would I go about holding them to it?

Is there something I'm missing here?

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Can I get a refund if my flight itinerary is changed?

Once you've decided on a new flight, call the airline to get your itinerary switched. If the change is significant enough and there are no other flights that work with your schedule, you do have the option to request a cash refund (even with a normally non-refundable basic economy fare).

Will BA give a full refund?

If you have booked directly with British Airways and you notice a mistake with your booking after you have paid for your ticket(s), you can cancel your flight booking and claim a full refund without penalty, up to 24 hours from when you make the original booking.

How do I get a refund from BA?

You will receive an email from us to notify you that you can apply for a refund online for the voucher you hold. Refunds can be requested via the online refund form. You will receive separate notifications for each eVoucher via email. You will need to complete a refund form for each one separately.

What are the cancellation charges for BA?

As mentioned above, the British Airways flight cancellation charge is zero if the cancelation is made under the 24 hours rule. However, the cancellation fee for cancelling the flight with domestic travel is $125 and its $450 for international travel, call on 802-308-3254 for cancellation fees.

Why can airlines change your itinerary without asking and what can you do about it?

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