Complex sentence: After becoming aware of this oversight, Seuss himself called Ravenscroft and apologized profusely and later wrote letters to columnists nationwide telling them that it was Ravenscroft who provided vocals for the musical number.
Split into simpler sentences: After becoming aware of this oversight, Seuss himself called Ravenscroft and apologized profusely. He later wrote letters to columnists nationwide telling them that it was Ravenscroft who provided vocals for the musical number.