Welcome to Vodafone Community
I can understand that it's frustrating not being able to get 4G which is so much a better experience when using your phone.
May I please ask these questions.
1. Are you in a 4G catchment area ? You can check by using the network status link Here.
Do you not get 4G even when commuting and the area is known to have 4G.
Vodafone also have a help thread with an included template which might help especially if you can copy and paste your answers to the template back here for the Vodafone Social Media Teams to look at.
May I assume you receive 2g and 3g so your Apn Settings should be fine.
Therefore it might be beneficial to check in your phones connection settings that 4G / Lte is ticked.
Also customer service can check your account to ensure 4G is activated as we did have some threads not too long ago that had people who had payg accounts that didn't have 4G activated on them.
Another good process of elimination is to try your sim card in another phone and another sim card in your phone.
Current Phone > Samsung Note 9 _512Gb > Model: SM-N960 Hybrid-Duos.
Samsung One Ui / Pie.
Samsung Gear s3 Frontier Watch.