You had a series of small issues but you should certainly complain. Personally I would have hit the nuclear button a little earlier - specifically, the point when sandwiches were offered to positioning crew when my tray was still empty - but I know it isn't always possible at the time.

I presume you have the receipt for your economy catering and the ticket receipt for your business class itinerary?

Write to Customer Relations (the contact details are in the contacts section in the main sticky) and be clear about what you want: a refund of the £3.50 or a cash refund of the first sector of the ticket or an amount of Diamond Club miles or whatever.