If they have an offset of ET35 without the full spec details and VW part number on the reverse side, they’ll be replicas rather than genuine Monzas, which probably explains the confusing / conflicting PCD details.
Replicas of the genuine article are often described by the seller as ‘Monza Style’ alloys or ‘Replica Monza’s’, They'll also often have other differences compared to OEM wheels - e.g. larger centre bore size so the wheels can also be used on a wide range of other manufacturers cars (with an appropriate sized spigot ring fitted inside the centre bore), and the offset is usually more aggressive than OEM to give a wider stance.
The offset of the genuine OEM 17” Monza alloys for the Golf is ET51, and they’re a 7.5J wheel. PCD 5x100 is the correct bolt pattern for the Polo, and the OEM 17” Monza alloys for the 6R Polo GTI are a 7J wheel, but they weren’t produced with such an aggressive offset as ET35; it was ET46.
If you’ve been told they won’t fit your Golf then that’s correct if the PCD is 5x100 as that’s the bolt pattern for the Polo.