Deducting pension from ESA

I was migrated from Incapacity Benefit to CB ESA in 2013 and then in 2015 I was awarded an IR-ESA top-up (which I should have received from the outset) but my £12/week pension was deducted, so I only received £1.49 IR-ESA. My pension is currently £15.18/week and I'm not certain exactly how much IR-ESA I receive as the letters don't separate the CB-ESA and IR-ESA amounts, but it's probably still around £1.50/week.

Looking at this page on the CAB website, it says that a pension is only deducted from ESA if it's over £85/week, so have the DWP erred by deducting my pension from my ESA? www.citizensadvice.org.uk/benefits/sick-...ow-much-you-can-get/