Airline ticket query for removal of one letter from my Surname.

Hellow Peter.

I bought a ticket through Mytrip travelling agency from Johannesburg to Cuba on the 23rd Aug to travel in Oct 2019. I immediately notice that I made a mistake of adding an additional letter at the end of my Surname. I have been attempting to change this one letter extra for two weeks now with no assistance. Mytrip is saying there is nothing they can do I must forfeit the money as there is no refund on that trip. The ticket is R17000. I have been moved from Arline to Mytrip so many times but I am still not getting assistance.

Please HELP!