I have a booking with a colleague made in august for BRU-AUH-DAC in november in Etihad business class.
Etihad has cancelled the entire booking as apparently they will not fly to DAC anymore.

As per EU 261 regulation I am supposed to be offered the choice between a refund, re-routing or rebooking on alternative dates.
I have contacted them on several ocassions by chat as well as by telephone. In the end after them pushing me to ask for a refund myself, they are offering to rebook the AUH-DAC legs on Air Arabia. Obviously I refused as this cannot be called 'comparable transport conditions', as Air Arabia only has economy class.
I believe that if they refuse to rebook me on 'comparable transport conditions', for example on TK or QR, I have the right to book a ticket myself and demand the fare difference in compensation from Etihad. However I have no idea how to get something in writing from Etihad, as I will probably need proof that Etihad was only willing to rebook me on Air Arabia,as well as I will need Etihad to refund the ticket unilaterally.
The fare was relatively cheap (around 1800 EUR) so obviously I prefer not to cancel and get a paid decent alternative.

What do you guys suggest I should do?