Some of the advice given was probably by Builders that have had personal experience of Boundary disputes,There's certainly plenty of unqualified people, they know who they are!
Boundary Disputes can be very lengthy and costly so it is better to sort the problem out before the legal profession is involved.
The OP does not say the age of the property or when the guttering and Ornamental pillars were fitted, if these were fitted when the property was first built then IMO they are part of the property and within the boundary, however if they have been fitted recently then they could be encroaching the Boundary,
As someone said earlier " Pictures speak a thousand words"