Is that a big deal?

The other day, I was with my friend in a coffee shop.
After we had seats, she asked me something with a bit bewilderd face. ( she is from England, by the way.) Actually, she asked me to ask stuffs to put some milk in her cup of coffee, because she doesn't like milk, which isn't in fact milk at all but kind of quasi milk and is usually served for coffee or tea here with a plastic package. So, as a quintessensial Japanese gentleman, which I mean me, I stood up, approached over them and asked,"Would you like to put some milk into her coffee?". But, a stuff, who seems to be a part-timer with a typical squawky voice, said, " I am afraid to say to you, but sorry we can't do that".

Partly because I wanted to be seen as a dependable person, and partly because I saw packs of milk behind the counter, I pushed up and insisted, "Please!"
Poor part-timer, realizing she doesn't have any authority over such a grave decision, walked away from us to the corner of the shop, and asked her seemingly boss.
A couple of seconds later, she came back to us, and again said," I know you don't like what I am going to say... but I am truely sorry that we can't do that".

I don't think I am either mean or persistent. But because I wanted to be seen as a reliable person, because I saw canteens of milk behind the counter AND because I couldn't believe that I need to ARGUE over this trivial things, I begged her to put milk into her cup. "Could you please put some milk for God sake?" Again, that bemused part-timer excused herself, walked over to her frown boss and whispered to her ears. After a couple of minutes, she came over to us and declared as if she passes some kind of judgement to the plaintiff who are indicted on suspision of tresspass or something," Okay, here you are, your milk!".

Maybe you would think this situation as typical Japanese scene, but the story didn't end with this yet. After she put milk into my friend's cup, she opened her palm and said "Here is your 20yen!!". We didn't get what she said so asked her what it is, which made us baffled.
"Now that you have some milk to your coffee, this became Cafelatte. And because Cafelatte is 20yen cheaper than coffee, you can take this!!".

This is neither joke or make-believe story, this really happened to us. Yeah, the fact that Cafelatte is 20yen cheaper than usual coffee is quite astounding story, but the reality that they declined to put some milk three times, succumbed to our persisten demand ( after a cute part-timer walked back and force between strange custmers and a sulky boss) and still or nonetheres or whatever tried to give 20yen back to us because somehow her coffee transformed into cafelatte according to thier wierd criteria is completely beyond our imagination.

I know we don't order something out of the menu in Japan, but I want this country to be more flexible for custmers as well as a confused part-timer!!!