@Robert-Paulson what was the date of your purchase of VP 20? And are you sure that "a free update in the purchase agreement" did not mean the usual free updates (new builds) for VP 20? A screendump @Dexcon mentioned would be helpful indeed.
Build updates and numbered updates are different, so be sure to see which you are entitled to with your purchase. Any version of VEGAS is entitled to free build updates. For instance, VEGAS Pro 20 had 3 updates over the course of its life cycle that added new features, and one that fixed bugs, and these build updates come at no charge. However, VEGAS Pro 21 is a new numbered version, and that update does not come free to VEGAS 20 users unless you subscribe to the monthly/annual VEGAS Pro 365 program, which comes with all updates regardless of if they are build or numbered version updates.