And still I don't think it is a problem. CIC gives you points based on your total work experience (multiple NOC's are allowed). Hence, you have nothing to worry about. Just provide the letter that says you were paid in cash and also any other evidence (work emails, even photos at work, just anything) that can prove your case, I think you are good to go. All the CIC officer needs is what to back up your work claims........the person pointed our payment evidence does not mean it is limited to that.I have two different NOC one as a software developer and the other as a teaching assistant and graduate research assistant. I picked the software developer one as the main NOC since I have a good reference letter matching the requirements. I hardly have 3 years experience in that NOC while the remaining experience belongs to the other NOC.
Please make sure you submit before the timeline given to you. Otherwise, you will most likely be refused.
Goodluck!!!