Compulsory top-up or at times, compulsory data subscription, is something imposed by many dealers (not the telco themselves). It seems legal for them to do this probably because they've overheads like rent and stuff to pay. Anyway, if you want to avoid it, go to a telco center instead, like Maxis Center though not many of these are in/near shopping malls.
Hotlink FAST had the option to payable validity extension when it's first launched, but Maxis removed it when they started giving the free weekend high-speed data sometime last year. Not all dealers have good product knowledge, so it's not surprising that the one you approached wasn't aware of the removal.
It's been shared a few times over the last months how to extend the card's life through timely RM5 reloads. It's quite similar to the recent sharing about extending same for the DiGi Best card.
Anyway, I personally won't call the experience "being conned", as it's happened to me when the older #Hotlink was launched and it's the first Hotlink plan without Validity 365. I just took it as a lesson for choosing the easiest way out by buying from the first dealer I came across while shopping, without doing my homework.