Documents not being issued even after serving notice period.

I work at an LLP startup in Bangalore. I was taken into the company through an internship at the CEO's own company based on my performance. The job market was not good so I accepted the offer to join the LLP company. I asked for offer letter right from the day I confirmed my interest. They said they was restructuring going on so would soon give the offer letter. It has been 1.2 years but I have not been given the offer letter or payslips. The only proof I have is the salary being credited from the company account. In January 2024, I asked repeatedly for my offer letter and I was told offer letter and payslips would be given when I am leaving. This was done to another employee who left in 2023 also. In March, I sent a resignation email stating I would be serving 1 month notice period as per the company's policy and my last working day would be in April. I asked the HR to send an acknowledgement email as a reply but said she cannot until the CEO approves. I have now completed the notice period and am asking for the documents but the CEO says they need a confirmation from a client that the project I worked on is working as per their requirements. I have not signed any documents that say I would have to wait till the customer is approving any project. The CEO also said the documents cannot be immediately given on the last working day but they will be given only after they have cleared any pending dues and have conducted an exit interview. I have been following up on the schedule for the exit interview but not getting any response. I asked the HR to at least give me the offer letter and payslips since they are documents that need to be given irrespective of resignation, but the HR is asking for approval from CEO who is not responding to the messages related to this matter. I am sure I am not at fault as I have rightfully completed the notice period and delivered the tasks and done the handover of files. I need your advice on this