Excuse me - Difference between"Shitsurei", "Osoreirimasuga" and "Kyōshukudesu"?

I understand "Shitsurei" means "excuse me" (is shitsurei a general context way of saying "excuse me?"?), but what about "Osoreirimasuga"?, apparently it means "Excuse me?" but i've never heard of it before, is it a really formal way of saying "Excuse me?"? What context would it be used in?
Also how about "Kyōshukudesu?", this is apparently another way of saying "excuse me?" but i've never seen it before, when and how would it be used?

Shitsurei / Shitsureishimashita
I'm sorry./Excuse me. (when apologizing for something the speaker did/said)

Shitsureishimasu
Goodbye./I'll excuse myself. or May I come in? (when leaving or coming in there)

Osoreirimasuga
Excuse me,~/I'm sorry,~(when asking for the addressee's help)

Kyōshukudesu/Osoreirimasu
Thank you. (when thanking for the addressee's help/words)

thanks