Can't connect to 1&1Ionos - Tried everything

[eggybread1]

I have hosting with 1&1Ionos. I have successfully been using Filezilla to connect. I'm on SKY broadband and occassionally I just can't connect at all so I connect using my mobile phone hotspot. Now that has started not connecting too. I have tested the connection at https://ftptest.net and it succeeds. I don't have a great understanding of all this but I've tried everything. When I run the Network Configuration Wizard in Filezilla I get:

Response: 230 logged on. Checking for correct external IP address IP 192.168.0.13 bjc-bgi-a-bd Response: 510 Mismatch. Your IP is 90.216.250.44, ja-cbg-cfa-ee Wrong external IP address

I've put the IP address: 90.216.250.44 in on the wizard and then I get this:

Checking for correct external IP address IP 90.216.250.44 ja-cbg-cfa-ee Response: 200 OK Failed to create listen socket on port 0, aborting.

Same thing when I try connecting through my mobile hotspot. I rang 1&1Ionos and they wanted to move me from Windows to Linux. I have websites which use Asp.Net framework. Do i really need to switch across to Linux? I don't know if that will fix this issue or wether my websites will still work? They want to charge me £20 for doing that too! It's just weird because it seems to be a temperamental issue thats gradually got worse and now I cant connect at all.

Any help is much appreciated.