That's not really suitable in this context - presumably, you are apologising for bumping into someone or the like. The simple past would be used in "I didn't see you".
"I haven't seen you" would be used in contexts such as "I haven't seen you before in my office; who are you?".
No, "Sie" (capitalised) only means formal "you", while "sie" (lowercase) means "they, them" and also "she, her".
At the beginning of a sentence (where the first word is always capitalised), you can't tell the difference, but in this one - with a capital letter in the middle of a sentence - "Sie" can only mean "you".
Answered two years ago — see mizinamo’s response to tokro. I will quickly take this opportunity to thank the amazing contributors who bother to take the time to answer questions. Without them, I would be lost. Please know that I very much appreciate responses to my own questions as well, even if I don’t respond with a reply. Lastly, a couple of times I have fired off a report and then realise my error. I wish there was a chance to recall it. I feel bad for the people who have to wade through all these reports. My apologies.