I had the same problem and got the following response from raising a support ticket 4962832:
Thank you for contacting EA help. My name is Rakesh and I would assist you with your Star Wars: Galaxy of Heroes issue today.
Matthew, I hope you're doing great, apart from this issue. Upon reviewing your case, I came to know that the Grand Arena Event is not available on your account. I realize its indeed disappointing. I'll certainly help you with the best possible information.
Matthew, we have checked your account details and cross verified this issue with all the available information. It looks like an emerging issue, can I ask you to please post this issue on the Star Wars: Galaxy of Heroes official forum, so that the studio team can look into this and they can correct this issue. Thanks for reporting this issue to us.
Forum link: https://forums.galaxy-of-heroes.starwars.ea.com/
I also saved this information for the studio team review.
This is to summarize, you have contacted us regarding the Grand arena Event Availability issue and we have provided you relevant information above.
Thank you for your time and kind cooperation with us.
Happy gaming and take care!
Should you have any further questions regarding this or any other issues, please do not hesitate to let us know.
You can also find answers to common questions on our Help Center at "http://help.ea.com" or ask our community experts by visiting Answer HQ at "http://answers.ea.com".
Thanks again for contacting EA help.
