No one ever said the vaccine would prevent transmission. What they said was that it !could! prevent transmission. But no one would know before studies were done. What they did say is that it would lower mortality rates. Which it did in fact do. But the factors of transmission and spread were dice rolls. And everyone with first hand knowledge knew that from day one.
But, you are in fact correct, you were lied to. But not by anyone with knowledge of the vaccines, but by the grifters you hold up has being "a beacon of truth". The grifters who read "Vaccine has a chance it could slow or stop transmission" and turn around and say "They are promising it will stop transmission!" just so they can tear it down later as "another victory for TRUTH!".