Your listing shows a postage charge to the buyer of £2.70 - that amount will have been paid directly to Ebay for the label you didn't use.
Eventually, that amount will be refunded to the buyer.
To change the tracking, you will have to contact Ebay Customer Services - use the link below.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)