Hi @Daks321 and @Francesca_Dnt, welcome to the Spotify community!
When we subscribe to Premium, Spotify sends us an e-mail with the purchase receipt. It contains the information about it, including usermane.
Please double check if you're logging in with the correct credentials.
Besides, you can check here if you have more than one account (and logging in the wrong one).
If you haven't received the e-mail, it's most likely because the purchase wasn't complete, and the charges will be refunded in the next few days.
You can then try again using different browsers in your computer.
Let me know if this helps!
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Note: I'm not a Spotify employee.