Is the statement of the groom to his fiancée and the witnesses: "This contract is void, it is not to be taken, nor considered valid, as if nothing ever happened, and I disavow myself to God of my error. And now I want to renew the contract in the presence of the guardian and the two witnesses," considered a divorce, necessitating a new dowry, or is it only a renewal of the contract?

A marriage contract is not valid without a guardian (wali) and two witnesses. Remote witnessing is not considered valid by many contemporary scholars. Therefore, the aforementioned contract is invalid, and your declaration of its invalidity is not a divorce. The woman is not entitled to any of the dower (mahr) specified in the invalid contract if consummation has not occurred. Hence, there is no sin upon you in contracting marriage with the woman again through her guardian and witnesses, and this is not considered a divorce.