If an assessment roll is amended so as to raise any assessment appearing thereon or to include omitted property, a new time and place for hearing shall be fixed and a new notice of hearing on the roll given as in the case of an original hearing: PROVIDED, That as to any property originally entered upon the roll the assessment upon which has not been raised, no objections to confirmation of the assessment roll shall be considered by the council or by any court on appeal unless the objections were made in writing at or prior to the date fixed for the original hearing upon the assessment roll.