Tink, I can't help you with the MSC but it's entirely possible the payment is not late. If you did it in November, for example, and the company pays in approximately 60 days then it's due about now. In any case, unless they pay in 30 days it's not seriously late.
You already know to get your own email account and don't share it with anyone. Now you also know to never delete any job related emails. You can set up a folder for each of your companies and move all related emails into the appropriate folder and keep them forever, or at least years.
Do you not have a list of all the companies you work for? If not, it would be a good idea to start one now. Also, you might find a folder for each job very helpful. I make a manila folder for each job, keep my notes and papers inside, hold it in my open file until it's paid, and then send it to my paid file. If you do this, you can always fall back on your system.
I think your payment is likely to come through whether you figure out the company in advance or not. It's only one shop so I hope you're not stressing out over it. Look at it this way. You don't have any proof of the shop or notes on the shop, so why worry? Hope for the best.
Mary Davis Nowell. Based close to Fort Worth. Shopping Interstate 20 east and west, Interstate 35 north and south.