Is it Haraam to wear, not a silver nor gold necklace, but one from regular string with Qur'an verse? I've asked some Imaams and they told me it's not Haraam, but it is if I enter the bathroom.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Wearing a necklace and/or a bracelet is something peculiar to women as they use it as an adornment, so it is not permissible for a man to wear them as this is imitating women. The Prophet cursed men who imitate women and cursed women who imitate men, as reported by Al-Bukhari. This is in relation to a necklace that is worn as an adornment. As regards a string to which some Qur'anic verses (or chapters) are tied to it, then the matter concerns the ruling on amulets. There is a difference of opinion on this, however, the most preponderant opinion is that wearing amulets is prohibited because the Prophet said that it is Shirk (associating partners to Allaah) if one wears them.  

Allaah knows best.