Where should i send my I130 and I864 withdrawal letter to, for a pending case ?

Probably the better place to send it is the National Benefit Center since you have information that the case is there. The other address in Chicago is just the lockbox which collects the fees and forwards the case to the location where the work will begin to be done. Looking at the form numbers that you wish to withdraw, you are apparently the petitioner who no longer wishes to petition. If you and the beneficiary used the services of an attorney, you could ask him or her for a copy of the I-130 receipt. (There is no receipt for an I-864 affidavit of support form). Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.