Buy 3 or 6 or 12 or 24 installment

Hello To All
Now i want to buy monthly, installment 3 or 6 or … this depent about how much i have on tymit,if i have 400£ i can just buy for a 400£ installment 3 or etc,or if i have 400£ on tymit i can buy for like 600£ And paid it back installment 3… etc

Thanks to all

U can only spend upto your limit

So do i need to pay back my money to tymit,if i paid it in 1 installement,i buy at jun like 400 the end of jun do i need to pay all 400 or its paid