Firstly you should contact the "reputable vendor", explain the problem and ask him for a solution.
What format is the serial number (use 9 to denote a numeric and x to denote an alpha character). Maybe what you think is the serial number is in fact not the serial number
VS9, VS10+, VS X4 Pro, VS X6 Pro, MS PRO 7 VE, Paint Shop Pro X2, Audacity
Panasonic HC-X920M, Sony DSC-H1