Client eventually paid all outstanding invoices, but not the late payment charges. What do I charge?

I know elements of this have been covered in this forum, but in different threads over many different years.

A client of mine finally paid up for some long outstanding invoices but said they didn't feel the need to pay the late payment charges.

I wish to submit a MCOL claim for these and all the late payments they made to me, but am struggling to get my head around the charges and interest.

I was going to submit a claim for the late payment charges plus interest up to the point of payment.

However, as the late payment fees were not paid (despite a number of statements being recieved for one batch thanks to a credit control app I now use) these invoices are therefore not fully paid.

Should I therefore calculate the interest on ALL full invoice amounts from the date they became due to the day I file my MCOL claim?

If not, what should I do? Any help gratefully received as I cannot find a definitive answer for this part payment situation.

Also, do I simply add up the individual amount plus charge plus interest on each invoice (I'll do it on a spreadsheet so I can submit it to the court) and put that amount in the date box in the claim? I'm trying to get an answer from MCOL, but cannot get through despite long waits.