Hey there
Sorry to hear of your issues.
With 3g no longer available on Vodafone and EE, Three currently switching off (most done) and O2 having started their switch off, you'll soon only be left with 2g and 4g on your S7 device.
Your device is also out of support by quite a few years so my advice would be to consider upgrading to a device that is in support and supports 4g / 5g as a first port of call.
I am not employed by Samsung nor do I receive any remuneration as a Samsung Members Star.
My device is an S25 Ultra.