In all the British lit I have read over the years, I have never seen the word "dinning."
The general rule of English is that when a verb ends in an 'e,' you drop the e when you add 'ing.'
Dive -- diving.
Rake - raking.
Bite -- biting.
Dine - dining.
I don't think anyone was bullying anyone, and I am so sorry you took it that way.
I think we were gently teasing.
Teasing like that generally means you are liked.