Pension payments

I am 64 on the 28th of January and have recently checked out my pension amount and realised that I will be six years missing from my full pension as when I was able to work for two different employers I paid in to there private pension scheme and when I was made redundant from the second job I withdrew my pension and used the money to pay for some improvements to my home 
my question is how do I replace the money in to my state pension as for the last twenty years I have been claiming esa benefit 
the reason for me not being able to work is I have two health problems being epilepsy and six years ago my kidneys failed and I was on dialysis treatment for four years until three years ago when I had a kidney transplant 
I am receiving PIP at the basic rate