CI can drop due to lack of marketing if it's over 0. But, if the CI is lower than 0, I don't think having no marketing campaigns should decrease it. There must be something else on the backround that reduces your CI.
First of, you said you have had 8 cancellations - in which time period, out of how many flights -> what is the % of cancellations from all of your flights? And how about delays -how many minutes on averages do you have?
Then, how old are your aircraft and what is their condition?
Also, what is the morale of your staff? Have you fired them lately? If it's less than 70, you should give them a payraise.
And, finally, you have quite a small marketing campaign. With 6 732s your income should be at least $500,000/week, from which you should spend some 40% ($200,000) in marketing.