OK let see. I guess one thing you should definately do is to get an info pass and schedule that exactly 45 to 60 minutes or even 1/5 hour before your scheduled interview which you have lost the notice of it and make sure you make 2-3 print of that. Talk to those officer who help the visitors with questions and explain them exactly what has happened. I am sure the officer whom your file has been assigned to will be notified and I am sure they will use your info pass print paper to call you in for the interview. Make sure to write your A# on the info pass paper with the exat time of your interview (hour and Min), this way they can verify that with their system and it shows you had already received that. I don't think it is a good idea if you do it on monday because they might tell you to notify the 1-800 number and this might delay your interview but if you go there as if you are ready for the interview, they will probably use your info pass as the receipt. After all as I said before the officer can easily confirm the interview schedule on his/her computer. Well This is all I can think of at this moment.
By the way if your DO is busy and you can not schedule your info pass before your interview, well I guess you have to schedule that for any available time on monday.