I'm now boycotting a supermarket, not Tescos, because of a similar issue.
In my case it was meat.
I ordered an easy boneless chicken joint for roasting for a Sunday lunch. The kind that comes in a tin foil container you just shove in the oven. They sent me a substitute of jerk chicken.
On a subsequent order I asked for 3 packets of minced beef and I ended up with 3 packets of Italian style meatballs.
After the second occasion I complained, that it was annoying having to send inappropriate meat items back, because it screwed up my meal planning. I asked them, very politely, to have a word with their pickers and suggested that their computer system was giving ridiculous suggestions for substitutions.
I was told that I had to put a note with each order if I wanted a particular substitution and that the pickers made their own decisions about substitutes.
I wrote back that I didn't think that was a reasonable thing to ask and that it was common sense to replace mince with something mince like and a roasting chicken with something you would eat with a Sunday dinner and not with something you'd have on a barbecue.
They basically told me their pickers were adequately trained. I'm assuming it was by Letitia Cropley. They gave me a voucher but I didn't spend it because they must feel my wrath for ever more!
So no YANBU!