Good day to you all

I booked TLL-HEL-LHR some months ago and reserved seats 18A for TLL-HEL and 6L for HEL-LHR. Few days ago I noticed that I've been moved from 18A to 17A, not a big deal as it's a short hop. Then my seat allocation for HEL-LHR disappeared and get a message that seat will be allocated at check in.
I contacted CS via Live Chat and agent said I can only reserve seats for extra payment or get a random allocation at check in. Tried to point out that I was able to reserve seats FOC while booking; there is no option to pay extra for seat reservation and that I still have seat reserved without a fee for TLL-HEL, but got the same answer that all seat reservations have to be paid for.
I'm not frequent on AY, has there been recent policy change that choosing a seat in J is for a fee? And if so, how my free seat reservation for TLL-HEL still stands even if it's Y?

Thank you all in advance