Denying Releving & experience letter

Dear Sir, I have recently changed my job. My notice period as per my offer letter is 2 months, which i had served properly.Though it it was agreed between my manager & me ( on email ) that my resignation is accepted subject to below 2 conditions - 1) Final Accounts will be completed & ready for signature. 2) 1 resource is trained side by side for 1 month. I have successfully completed both the above task during my notice period. Every single day i used to update the status to my manager on the progress. Meanwhile they had given me Tons of other work simultaneously saying you are senior you have to do it. So i had to do all of them as well. After working days & night in my notice period, i had send the final accounts copy to the auditor on my last day & copied my manager too for confirmation. My manager has told me you do as much as you can & we will handle things after your exit. The HR on my last day had send me mail saying your Relieving Letter & Experience letter will be given to you subject to feedback from manager & salary slip of new company. My manager had told HR that i will give feedback after 10-15 days, so i wanted until that. Now when i have emailed my salary slip to HR asking for my documents that are saying your work ( preparing SOP - standard operating process) is not yet completed please complete. Please complete is then only we will release document. i don't understand SOP wasn't agreed still i made it for them during my notice period itself, now they want some formatting & addition of content so they have stopped processing of my documents & have send me mail asking me to complete SOP. i am unnecessarily being harassed & they always harassed my during my tenure as they knew how hard working i was so task of everyone else was given to me. Just because i love my job & passionate towards my work will this happen to me. my question is why i wasn't told this on my last day why did they wait to get additional task done from me after i exit.