Regarding interest of outstanding dues of employee

I was working in a PSU. I have to leave the job as i was suffering from lumber sacro disc problem coupled with pressure from organization to join back.
I have resigned online which they accepted retrospectively condition of 1 month salary and any outstanding dues (which i considered nil).
When i approch them after 3 years they informed me amount of 5 times of my 1 month remuneration and around 50 documents (not listed). But my query of to whom to pay was left unaddressed by them. Also i filed a online transfer claim application to my new employer pf account.
Till date i never recieved a demand letter and last month, after filing cpgrams for non transfer of pf in last 3 years, i got call that they will charge interest on dues and question on documents left unsolved.
Please provide from whether they can charge interest without providing me the information related to total dues? If yes then which time period will be considered?
Also they maintained a PF trust with them, they refuse to provide me pf without settlement of dues. What is needed in such situation?

Query is not clear.
"I have resigned online which they accepted retrospectively condition of 1 month salary and any outstanding dues (which i considered nil)."
Have they given written acceptance of resignation?
What you consider about o/s dues is alright, but what is the record of PSU about loans, advances etc
You will have to write query more clearly and chronologically for better answers.
Why you waited for 3 years is also not clear?

Resignation was accepted in 2013 and as there was no communication by them regarding my dues and also I considered my 1 month pay would be adjusted with PRP (which they provide).
I had to withdraw my savings from their trust so I approached them. Even today while asking for demand letter they got annoyed on the mention of demand letter.