Disappointed 😔

I bought two grey school pants for my kids last month to prepare for winter as the schools re opened yesterday they tried them on and the pants were too small, can’t find the slip, I payed with my debit card hoping they can trace as it’s only a month ago , emailed their customer care and just got a reply that they can’t help just like that no call nothing, the pants are new I good condition still with price tag on as they were not worn so what must I do as I am unemployed and can’t afford the new pants am so disappointed as I am their customer and do my shopping with them.. very disappointed with their customer care 😔