PPI - Please help

I have found an Annual Review of Optional Payment Protection Insurance on my mortgage, this form gives me the information on about how much this insurance has cost in the past year and how much the estimated total cost of PPI for the remainder of the loan agreement. which is £7,257.62. I no longer have this mortgage as I sold my house to pay off HMRC (another nightmare) How do I claim this money back? I wasn't aware of what this meant at the time but as per Martin Lewis' advice on This Morning, I thought I'd look into it. I haven't been able to do anything previously due to mental illness and now looking after my parents and trying to hold down a job.