Follow the list;
I’m really / terribly / so sorry for being late. It won’t happen again.
Please excuse my late response.
I apologise for not calling earlier. and etc…
Follow the other expressions;
43 Ways to Say You Are Beautiful in English
English Ways to I LIKE IT
Do You Want to Speak English Faster?
CHAT ABBREVIATONS in English
Words To Use Instead Of VERY in English
Collocations in English - GO and HAVE;