I had an assignment in a hospital which could not be completed because the client was not there. I e-mailed the Mystery Shopping Co. and they paid me the full fee.
Another time, no demonstration was scheduled by the warehouse store, I e-mailed the company, got much up and down the ladder communication, etc. They agreed to pay, posted it but still no pay, my fault, I'm too tired to fight.
A third time there was no Valet Parking at the hospital's emergency entrance, I called the MS provider from the site. They said to go ahead and do the available Valet parking, I did, got a ten rating and three weeks later got turned down by the Client, who said no pay. The MS Co. offered to pay me the $12 from their pocket. To save their face, I accepted.
From these experiences I've learned not to delete e-mail or I print 'n save it in an envelope file.
I wish you success.