THY Refuses to Change My Ticket for an Urgent Return

I purchased a round-trip ticket from THY for LAX-Istanbul, Istanbul-LAX months ago for $1200. Due to the passing of my fiancé's grandfather, I changed my departure ticket to fly from Seattle to Istanbul, the first place I was at that day. I paid $130 for this change and encountered no issues. Now, I urgently need to return because my school and job continue in America, but they claim that I bought the Seattle-Istanbul flight too 'cheaply' and therefore cannot make changes to my return flight, stating my class is too low. I explained that I had a funeral and would have paid $1000 for a ticket from Seattle that day, and that my departure ticket should not affect my return ticket. My original plan was to travel in July and return in August, but I had to return due to the funeral, which was not a leisure decision. The unhelpful attitude of the call center and the lack of assistance in this process is truly unbelievable. Even though I am willing to pay a penalty fee, they say my ticket will be forfeited or that I must use my return from Istanbul in August. Their unhelpful attitude, especially for a non-leisure situation, is very upsetting.