Samsung Flex device returned - Finance still not closed

[Uac25]

I returned my S24U through the flex programme on 4th Feb and it was received by the MTR company who deals with the devices on 6th Feb. I received an email confirmation confirming that the device was returned and it would take 10 days to close the finance agreement with Samsung Glow. 
I've contact Samsung CS on several occasions and I have been told it's been escalated several times to the upper departments but my finance plan still hasn't been closed and I am expected to pay the next payment despite not having the device anymore. 

Has anyone else gone through this issue and if so how were you able to resolve it? 

[Obsydian]

When i had the scheme prior to Flex, i had the same issue, but I just cancelled my standing order, that was I think the ZFOLD3, but with the ZFOLD4 is was seamless, but as I said, the scheme before Flex came into being.

Be mindful when cancelling the Standing Order or Direct Debit, been though your paid up, if they did try and charge it would reflect in your credit rating.