If you were offended by the "gift," then you did the right thing to report it. A single incident like this, however, without more (you don't mention any other incidents), is almost certainly not going to rise to the level of sexual harassment (or sex discrimination) under the law. As far as what the company "has" to do to investigate, if they determine that the conduct you reported on its face does not rise to the level of sexual harassment, they don't legally have to do anything. But they...
1 lawyer agreed with this answer
Absent an employment contract (individual or union collective bargaining agreement), the general answer would be yes, your employer can change the terms and conditions of your employment, including your rate of pay, at any time (going forward; your employer cannot *retroactively* change your pay without running afoul of wage-hour laws). Nor can your employer take any adverse employment action (which would include a pay cut, obviously) against you *because of* age, race, sex, disability...
1 lawyer agreed with this answer