Terminated workman from giving 2 PIPs

I was working in a corporate firm for 1yr. They given the workman one 30day PIP and 7 day PIP. Given me time to resign for 7 days. I was working badly to pickup sales of the product worth more. Target given to me was not at all accomplishable in my area which they planned to take my job as a fresher who needs help for picking up in field. I found no documentation policy from company offer letter. I asked them for policy and thry dont have it. Many workmen were given PIPs just changing targets in conference calls rather than any written documentations emailed. I believe than PIP is an internal policy of company which shoulf be in a contract form signed by employee but none seen here but just a PIP initiation mail and a termination letter. I have proofs of seeing customers in my area in every corner of given area with their ph no. But none were taken into consideration rather than sale number which is not at all acheivable. Any way to get reinstatement back my position. Any ways to ask PIP contract or PIP documentations