2018/19 = £5,724 + 3.7% bonus(applied on 1st April 2020) = £5,935
From April 2019 pensionable pay and contributions increased by 3.3%, as a result of the changes in 2014 which de-linked pay rises from pensions.
Therefore:
2019/20 = £5,915
From April 2020 pensionable pay and contributions increased by 2.4% as a result of 2014 changes.
Therefore:
2020/21 = £6,059 for a full year and aprox £3,534 for 7 months worth.
Giving you a total DBCBS of aprox £15,384, which is £105 less than the amount quoted on your attachment. I have no definite explanation for that difference to be honest.
*The next DBCBS increase will be 1.7% which will be added to years 2018/19 & 2019/20 from 1st April 2021, and therefore I assume, will not apply to you as you've already taken your cash. Unless the £105 was a pro rata amount applied to your balance when you left?