I'd want cash. You should not have to accept vouchers or miles. This is not a goodwill thing they did not provide the product as described.

If you were sold the upgrade shortly before the flight and you were not warned about the slight downgrade from the well-publicized product description at the time, I would say you do have a case and should not have to accept vouchers or miles but some cash back.

I would have also been far more disappointed about the lack of the expected level of food and especially the lack of coffee menu, more than you would think, compared to the value of the items you did not receive. Despite your disappointment, which I do feel I would have as much of as you on these seemingly trivial items, I think you are owed only a relatively small proportion of the cash back.

Why not respond to them requesting the 100 euros in cash. True, what you missed is probably worth 20-30 euros at most, but there is the shock of disappointment etc., not being told when they already knew before the flight the full service was not provided and did not tell you (misrepresentation etc.)., so you could ask for 100 and then consider how much less you would accept.

If you speak German could be worth looking on some of the German / Austrian forums because it is sure others will be reporting this issue.

If a chargeback is going to harm your own credit record then "don't cut off your nose to spite your face".