Player going through wall

Hi,

I am making a small bumper car game. I have set my walls up as cubes with RigidBody and Box Colliders as shown in the picture below.

https://i.gyazo.com/d41c4e388117f1c2a2b0da30a7692530.png

My bumper car object is configured as follows:

https://i.gyazo.com/0bd14261211018e315e83d6abf75a3bf.png

As long as my player object (bumper car) is moving fairly slowly, everything is good (bounces off the wall, and stays within the designated area).

However, when the wall is hit at speed, the bumper car simply passes through it and hovers out in the void.

I have tried using rigidBody, colliders and adding mass to both wall and player, but nothing seems to work.

Any help is much appreciated.

Edit: the script I use to control player movement is this:

 using System;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class PlayerController : MonoBehaviour
 {
     // public Text countText;
     // public Text winTexy;     
     public float speed;
     private Rigidbody _rb;
     private int count;
     
     private void Start() //run-once code
     {
         _rb = GetComponent<Rigidbody>();
         count = 0;
     }
 
     private void Update() {
         if (Input.GetAxis("Horizontal")>0) {
             transform.Rotate(0, 5, 0);
         }
         if (Input.GetAxis("Horizontal")<0) {
             transform.Rotate(0, -5, 0);
         }
     }
     private void FixedUpdate() //physics code
     {
         var accel = 50f * Time.deltaTime ;
      
         if (Input.GetKey(KeyCode.UpArrow))
         {
             //Move the Rigidbody forwards constantly at speed you define (the blue arrow axis in Scene view)
             _rb.velocity += transform.forward * accel;
         }
 
         if (Input.GetKey(KeyCode.DownArrow))
         {
             //Move the Rigidbody backwards constantly at the speed you define (the blue arrow axis in Scene view)
             _rb.velocity += -transform.forward * accel;
         }
 
         if (Input.GetKey(KeyCode.RightArrow))
         {
             //Rotate the sprite about the Y axis in the positive direction
             transform.Rotate(new Vector3(0, 1, 0) * Time.deltaTime * accel, Space.World);
         }
 
         if (Input.GetKey(KeyCode.LeftArrow))
         {
             //Rotate the sprite about the Y axis in the negative direction
             transform.Rotate(new Vector3(0, -1, 0) * Time.deltaTime * accel, Space.World);
         }
     }
 
 }