"mortified at" is correct and usable in written English.
You can use it to express deep shame or embarrassment. For example, "I was mortified at making such an embarrassing mistake."
He is mortified at having killed her.
"At first he was mortified at training with United.
"I was mortified at what had happened," Kinney said.
Rubina is mortified at having to call her host to ask for a second invitation.
I'll take it.' Though I would have been mortified at the time".
Poor Rhoda was mortified at having to bend over during a difficult birth.
As a people we should be mortified at the quality of our representation.
When he saw us, he shot up, looking pleased and mortified at the same time.
He was mortified at the rebuff, and his attitude toward Peel and his brand of Conservatism became increasingly critical.
Yet they are as comfortable with their nakedness as I would have been mortified at the same age.
The pope, mortified at feeling desire for the woman, ordered a servant to cut off the offending hand.
