Can't buy KIT for The Sims 4 EA error (ref. #54005)

I'll start by saying that I've already followed all the steps recommended in this post by EA_Solaire. A prepaid credit card is linked to my Paypal account, which I've always used for purchases in the EA app. However, since last Friday it has inexplicably stopped working and keeps giving me an error. I waited until today, which is Monday, to see if the situation would be resolved, but no luck.

I'd even opened a chat with EA Help, but all I got was automatic replies that didn't resolve the problem and then the case was closed with the words Fixed, which didn't happen.

I just want to be able to purchase your games, but if you don't allow it because there are technical problems on your end, it's just your loss. And before you ask, there are enough funds, a KIT is €4.99, and on the prepaid credit card there is €20.