Full and Final settlement issue - company paid me more than I served

Hi, I have resigned my last organization on 8th Oct and sent mail to my line manger by marking cc to HR head stating that I will serve notice period of 16 days and will work till 23rd Oct. But they didn't bother to revert and my online portal request for resignation also not accepted. I reached my HO on 24th for submitting assets but no one bothered to accept and HR insisting me serve till 6th Nov to complete 30 days. But as per my appointment letter it is mentioned that I need to serve 30 days notice period or give pay to Company.
So on 8th itself I requested my Line manager and HR to adjust my leaves but no response. I tried a second attempt to convince HR on 25th but they said we will accept assets but don't give relieving and experience letter. So I had submitted laptop and taken ok from IT by marking mail to HR. So my last Day became 25th. On 27th my line manager accepted my resignation by making 6th Nov as last day. Now on 9th nov I got several mails from them that my that my exit clearance form approved by admin IT reporting manager finance and even HR as well. Even got a link to submit exit clearance which I completed. Today I got F&F calculations and as per it they have considered my last day is 6th Nov instead of 25th Oct and paying salary till 6th Nov.
My questions are
1. How come they are paying me for days which I didnt work.
2. Will they give me my releving letter and experience letter.
3. What should I do as they add giving me excess amount for which I haven't served.
Help me urgently as they have asked Me to reply before 18th Nov to confirm. Or they assume I am OK with it.

Hi Vijay,
It is suggested to you that you bring this to the Notice of your HR Manager through mail or written communication seeking clarification on Point No.1. So that you are safe from your end and the ball is in their court.
Further,if you have completed six months and are a confirmed employee which you have not clarified to us.You are entitled to receive relieving letter / experience letter subject to proper resignation and handover of job responsibilities and company assets in your position.
If they fail to provide you a relieving letter / experience,please send an official mail to them (HR) stating that as per their records you have worked with them mentioning your designation and actual period of employment.This mail copy you can present to your new employer stating all the facts.
Please contact for any further clarification.
Best Wishes,
Sumeet
M-9967714245

I have worked for 2 years 3 months in that organization. I have been confirmed and even High rator in last appraisal.

You are entitled to receive Relieving/Work experience letter.Need not worry.