PPI Tax reclaim help

Lewes6

In 2018 I helped my mum claim back PPI in my later father’s name. 

In March 2020 I helped her fill out the R40 form to reclaim the tax on this however I don’t think I fully understood what I was doing and may have put the incorrect amounts in. The PPI amount that she received was £6188. Tax of £1237.41 was deducted by Barclaycard/HMRC I believe. I think I then miscalculated this when doing the claim and she only ended up with a tax refund of £198.01.
On the Tax calculation letter she received from HMRC in 2020. The amount of £6188 was listed as savings income and to the right the tax deducted (£1237.41) was listed. Does this mean I filled out the R40 incorrectly as this should have only been the interest earned and not the full PPI amount? Sorry if this doesn’t make sense but she has just received quite a large tax rebate (approx £1.5k) and I’m trying to figure out if this could be related to me filling out the details incorrectly as her income from her state pension and my late Dad’s pension hasn’t changed.
Thank you in advance for any help!

Dazed_and_C0nfused

Based on the tax figure £6,185 was the taxable interest (£6,185 x 20% = £1,237).

Most people would get a tax refund of under £200 so £198 seems perfectly normal.

What doesn't seem correct is the £1.5k.

Which tax year was the £198 for and which tax year is the £1.5k for?

Does the calculation for £1.5k include the £6,185 again in error?