EA app logged in old legacy account with me knowing - system bug/glitch

So I opened the EA app on my pc as usual, looking to play the Sims. There were no prompts or indicators to say that the app had signed me out of my main account and automatically signed in an old inactive account. So obviously I thought everything was normal.

Saw the new Bridgerton packs for the Sims 4 and purchased them. Loaded the game, I had all of my game saves, my families, but none of the previous packs I've bought and spent a load of money on.

Got in contact with EA and found out that the new packs were purchased on a different account. As I told them, I don't know how it's happened because the app never told me that I'd been signed out of the main and signed into the legacy. 

I repurchased the packs on my main account, but they won't give me a refund even though it was a system bug that caused me to buy them on the legacy account (which is so old I forgot it even existed, since I only use my main account). So they've had double the money out of me now and half is on an account that has been inactive for so long I couldn't tell you when I last signed into it.

EA have said they'll investigate it but that there's not a lot of reports about the system bug on EA forums. But I've seen it reported a bunch on Reddit and other sites. 

Please upvote if you've had this happen or have heard of it before.