One thing I have noticed Steam doing of late is they have been asking me my three digit security code, from the back of my credit card. They never did that before.
I had my account hijacked once before, and it did take about 4 days for the first reply from Support. Then, they did want my credit card number that I had made purchases with. I didn't see I had much choice but to send it to confirm who I was. Worked out fine, did take about a week total. Keep in mind, Support doesn't work weekends, either.

Ryzen 7 2700K, Asus Prime X570P, 32Gb DDR4, 2x 1Tb M.2 SSD's, RTX2060 6Gb, Occulus Rift
Win 10 Pro 64bit, keyboard/ mouse/ wheel/ pedals/ baseball bat
Security Coordinator on the Battleship Iowa