Someone has used my student credentials to get half price premium

[farhat]

Someone else (I don't know how or who) has used my student credentials (Unidays account) to gain half price premium subscription on an account that is not mine. I only found out when I tried to activate the discount for myself - and Spotify told me my credentials were already associated with another account/discount had already been applied to another account. 

After contacting Unidays with this issue, they gave me a discount code to redeem - but I cannot find where to paste this to redeem it - anywhere on the website/app 😞

Can someone from Spotify please help me I have been trying to get help for the past week with no resolution. How can I disconnect my credentials with this random person's account? And where can I redeem my discount code in the mean time?

I have changed my passwords to avoid any future fraudulent usage in the mean time too.