Last Friday, I received an email suggesting I upgrade my firmware. The model I have is the AX1800 Whole Home Mesh Wi-Fi 6 Modem Router Deco X20-DSL (that's what it says on the box anyway). So, assuming this email was valid for my modem, I dutifully followed the instructions to upgrade the firmware - oh, how I wished I hadn't! Immediately after, my internet connection was lost so now I'm using my mobile phone as a hotspot in order to access the internet. Unfortunately, my mobile data allowance is finite and I don't think I'll have more than a week's normal usage before my speed is slowed or I have to purchase more data.

Anyway, putting aside the fact that I'm extremely angry that a firmware update has done this, (I assume it wiped out all the ISP information which is why I lost internet) I need to get things get back working ASAP. I spent a very frustrating hour on the phone with one of their tech support people yesterday and ended up getting nowhere. The issue seems to be that in order to fully configure the modem via the Deco app, I need to connect to the temporary WiFi network it creates and also to the internet so I can login with my TP-Link ID.

The thing is, my Samsung Galaxy S20 FE is unable to use two active connections at the same time, e.g. if I connect to the WiFi, I lose my 5G connection, and vice versa. I also tried my boy's iPhone 13 but got the same result. So can someone please suggest how the hell I'm ever gonna get this fixed? Because at the moment, I can't see any way.

Thanks in advance for your help.

BTW, here's the main contents of the email I received last Friday:
 

Dear customer,

A new firmware upgrade is availabile for TP-Link HomeShield. Following the upgrade, if your device firmware is listed below as an older version, certain HomeShield features may not function properly. To prevent any inconvenience, we strongly recommend updating your device to a newer or the latest firmware version as soon as possible.

Model Old Firmware Version Suggested New Firmware Version
Archer AX90_V1 1.0.6 Build 20201020 rel.75204 and lower 1.1.12_build_20230526 or later
Archer AX73_V1 1.0.4 Build 20210717 rel.62921 and lower 1.2.6_build_20230526 or later
Archer AX4800_V1 1.0.1 Build 20210717 rel.66041 and lower 1.2.6_Build_20230526 or later
Archer AX4400_V1 1.0.1 Build 20210719 rel.58490 and lower 1.2.6_build_20230526 or later
Deco X20-DSL_V1 1.0.6 Build 20230303 Rel. 38090 and lower 1.0.12_build_20230714 or later