Formal and Informal Letters - Change of Register.
Here is one suggested version.
______Dear Mr. Jones_____,
______I regret not being able_____ to get to your business dinner last Friday. I was really looking forward to it and I was all ready to leave the house when _____a relative arrived unexpectedly._____ She was only in town for the one evening before she went to my brother's house so I had to stay with her. ___________Please accept my sincerest apologies.___________.
I tried to telephone you but your line __________was twice engaged____________ when I telephoned. ___________Later, I was otherwise engaged___________ and didn't have the chance to ring again.
___________I hope you can understand my difficulties___________. I know you wanted to _______introduce me to Ms. Phoenix____ ______________who you work with. ________I hope this will be possible at the next available opportunity_________. _______ ____________I hope the dinner went well for all concerned.___________________.
_____I look forward to hearing from you soon.______