Hi,
I was really upset when you did not visit me. I was more unhappy than angry.
I was really mad when you did not visit me. Angry but not usually in a very, very serious way. Also, not a formal word.
There are lots of synonyms, eg annoyed, cross, sore, put out, irritated. And there are many shades of meaning, in the words themselves and in the context.
Best wishes, Clive