Undue delay by previous employer causing delay in joining new job

Dear Sir, I have been selected in Bank Of India (BOI) as a PO via IBPS CWE VI. As part of joining formality they had send a questionnaire of 5-6 questions to my previous employers- WIPRO TECHNOLOGIES and STATE BANK OF INDIA,BANGALORE CIRCLE. While Wipro Tech. have duly reported back to BOI with the filled in questionnaire State Bank OF India has been highly reluctant to cooperate and send the details. They had initially thrown the request in dustbin when its was send via speed post on 11/06/2015 and when i inquired they claimed as never ever receiving such a speed post. As a result i had to request BOI to resend the questionnaire to them.Thereafter I followed up and on calling the manager HR SBI, Bangalore circle requesting for early resolution of the issue, he asked me not to call HR DEPT. SBI, BANGALORE again as its beyond my reach and they are not answerable to me. Also its only the BOI HR who eligible to talk to them. After lot of request they called on BOI HR dept asking for all my posting details while serving SBI (01-03-2011 to 18-12-2012 as PO) along with resignation approval copy.All such documents were send by BOI via speed post and received by SBI HR DEPT on 11th July2015. Its a week now and they have not bothered to send back the simple questionnaire as a result my joining is delayed indefinitely. Kindly advice me on the issues-