Glitchy connections--4G and wifi

I posted a shorter version of this message in another community posts as a response to someone else who had a similar problem.

I live in Cardiff, Wales and am having connectivity issues as does my partner on Vodafone. Spotty reception, shows 4G with bars. WiFi calling also not great (and our home has thick walls). My iphone was checked out by an apple tech expert and it’s in good condition. Additionally my phone seems to perform slightly better when I set it to 4G, instead of 5G automatic (5G seems to have very bad connections).

When I switched to Lebara, I got a text message from Lebara saying I needed to change the Mobile Data and Personal Hotspot settings from Vodafone (which automatically loaded with the Lebara Sim) to Lebara. But when I contacted customer service, it said the settings for should be Vodafone. The Visual Voicemail and MMS settings are to Vodafone.
So now I'm confused as to what to do. At the moment, the Mobile Data and Personal Hotspot settings are for Lebara.
I have reset my network settings in hopes things will improve.

I've checked on Speedtest app many times over the past few weeks and many times the Downdetector indicates problems with Lebara and Vodafone.
Please advise.
Thank you for your time.

Just changed it to Lebara's settings for Mobile Data, and see if it's any better. You can always change it back, it's not going to break anything - not sure why customer service is telling you to use Vodafone's settings, as that's just wrong according to Lebara's own instructions.
Visual Voicemail is irrelevant for Lebara, as they don't offer it.
If that doesn't make it better then Vodafone or any network that uses them probably isn't the best network for you.

Thanks, Tom. Have set that back to lebara. You may just be right about Vodafone. I’ll wait and see.