Phone is 4g mobile data wont even reach LTE most of the time

So I have been using id mobile for over a year and I used to have a really old phone which would go up to LTE. I was ok with that until I upgraded my phone to a Samsung A51 which is 4G. When i turn on my mobile data it goes to LTE. Most of the time it doesnt reach LTE and goes to H+. I tried to go into the data settings and change it to 4g only or 3g/4g(its on automatic)) So when i change it to anything that isnt automatic my data just doesnt turn on. My main problem is that i dont have anything higher than LTE and my data is extremelly slow on H+ signal. its rare for me to even hit LTE. I live in l26 1TR.  Please help as I really rely on my data and i need it to be as fast as possible.