[Python] Kinetic energy explodes while resolving collisions in physics simulation

I'm trying to make a basic collision simulation in 2D using python, but even in elastic collisions, the total kinetic energy seems to be exploding after a few collisions with each other, which should not be happening.

I'm using Pygame to display the simulation.

while running:
for event in pygame.event.get():
if (event.type == pygame.QUIT):
running = False
screen.fill((0,0,0))
for i in l:
pygame.draw.circle(screen, (255, 255, 255), (int(i.position.x), int(i.position.y)), i.radius)
#next frame calculations
i.update()
i.WallCollision(a-r, b-r, r, r)
for i in range(len(l)):
for j in range(i+1, len(l)):
l.Collision(l[j], 1)
print("Kinetic energy = " + str(sum([0.5*i.mass*i.velocity.ab()**2 for i in l])))

screen.blit
pygame.display.update()


These are my collision detection, updation and resolving functions.

class entity:
def __init__(self, radius: float , position: Vector2D=Vector2D(0,0), velocity: Vector2D=Vector2D(0,0), impulse: Vector2D=Vector2D(0,0), acceleration: Vector2D = Vector2D(0,0), mass: float =1.0, e_wall: float = 1.0):
self.acceleration = acceleration
self.velocity = velocity
self.position = position
self.mass = mass
self.e_wall = e_wall
self.radius = radius
self.impulse = impulse
self.dt = 1
def update(self):
self.velocity = ((self.velocity * self.mass) + self.impulse ) * (1/self.mass)
self.velocity = self.velocity + self.acceleration #* self.dt
self.position = self.position + self.velocity #* self.dt
self.impulse = Vector2D(0,0)

def WallCollision(self, x_max:float , y_max:float, x_min:float, y_min:float):
if (self.position.x > x_max):
self.position.x = x_max
if (self.position.x < x_min):
self.position.x = x_min
if (self.position.y > y_max):
self.position.y = y_max
if (self.position.y < y_min):
self.position.y = y_min
if (self.position.x >= x_max or self.position.x <= x_min):
self.velocity.x = -self.e_wall * self.velocity.x
if (self.position.y >= y_max or self.position.y <= y_min):
self.velocity.y = -self.e_wall * self.velocity.y
#self.acceleration = Vector2D(0,0)
def Collision(self, other: 'entity', e: float=0):
u1 = self.velocity
u2 = other.velocity
m1 = self.mass
m2 = other.mass
n = Vector2D.norm(other.position - self.position)
if Vector2D.ab(self.position - other.position) <= (self.radius + other.radius) and (u1 - u2).dot(n) > 0:

error= (self.radius + other.radius) - (self.position - other.position).ab()
if (error > 0):
self.position = self.position - n*(error/2)
other.position = other.position + n*(error/2)

k=(1/m1 + 1/m2)
j1=n*(1+e)*(u1-u2).dot(n)*(-1/k)
j2=n*(1+e)*(u2-u1).dot(n)*(-1/k)
else:
j1=Vector2D(0,0)
self.impulse = self.impulse + j1
other.impulse = other.impulse - j1


I can't seem to understand why the total Kinetic Energy keeps increasing.

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