Settlement letter at Nimble Collection Services (Thruworths)

I settled my account the lady who was assisting me was calling each an every day since I made arrangements to settle my account and promised that I will get a paid up letter as soon as the funds appears on their account. After sending my bank statement as proof of payment the lady suddenly became rood when I call to ask for a paid up latter and told me I must email proof of payment. But the payment was a debit order. They are now ignoring my emails. Hello Peter please assist.