Turkish Airlines complaint: Unable to pay for my reserved flight ticket

I book a flight with Turkish Airline to travel to LONDON from LAGOS, before the pandemic but was unable to travel that year, I clearly Turkish Airline the following year for refund but they said they don’t do refund but I can convert the ticket to voucher, the ticket was converted to voucher which has two years expiration

I intend travelling say for March this year and card Turkish Airline about the voucher and another flight ticket was raised and that I am supposed to pay back of $215 including amount on the voucher

I was about to pay and I was told I can pay from Nigeria that I should go to there end office in lagos, I went there I was also told to call the Turkish line concerning the issue

I was obvious that they don’t want me to benefit from the voucher and I have decided to travel through another flight so that they can refund me

Please kindly help intervene in this issue, I am ready to pay the balance of $215 or they should refund me my voucher money

Thanks