Struggled to change the flight date of a flexible ticket

No idea what happened, Travelstart used to be brilliant. I could contact them easily in the past via whatsapp but these days it's like no ones there sadly! I bought a return ticket and paid extra for it to be flexible due to me being uncertain what date I need to return for my brothers wedding. Now if I can't change the ticket to earlier I'll miss a very important and special day for my family. Just trying to fly by the 20th of April.