CNN implementation low accuracy on MINST data

I'm trying to implement VGG11 (Model A of Table 1 from this article) on the MINST dataset but I'm getting ~10% train test accuracy (as bad as random guessing). I had to resize the MINST data from 28x28 to 32x32 to fit the CNN architecture. This is what I did:

from keras.datasets import mnist
from keras.models import Sequential
from keras.layers import Dense, Conv2D, MaxPooling2D, Flatten
from keras import optimizers, utils
from PIL import Image, ImageFilter
import numpy as np
import tensorflow as tf

# Preprocessing

x_size = 6000 # Changed to reduce training time 
(x_train, y_train), (x_test, y_test) = mnist.load_data()
x_train_ = np.ndarray((x_size, 32, 32))
x_test_ = np.ndarray((x_test.shape[0], 32, 32))

# Resizing inputs to 32x32
for i in [0, x_size-1]:
    im = Image.fromarray(x_train[i], mode=None)
    im = im.resize((32, 32))
    x_train_[i] = np.array(im)
for i in [0,x_test.shape[0]-1]:
    im = Image.fromarray(x_test[i], mode=None)
    im = im.resize((32, 32))
    x_test_[i] = np.array(im)

x_train_ = x_train_.reshape(x_train_.shape[0], 32, 32, 1)
x_test_ = x_test_.reshape(x_test_.shape[0], 32, 32, 1)

y_train = utils.to_categorical(y_train,10)
y_test = utils.to_categorical(y_test,10)
y_train_ = y_train[:x_size]


# Model A (VGG11) of Table 1: ConvNet configurations from paper arXiv:1409.1556v6

model = Sequential()
model.add(Conv2D(64, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same', input_shape=(32, 32, 1), data_format='channels_last'))
model.add(MaxPooling2D(pool_size=(2, 2), strides=(2,2)))
model.add(Conv2D(128, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same'))
model.add(MaxPooling2D(pool_size=(2, 2), strides=(2,2)))
model.add(Conv2D(256, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same'))
model.add(Conv2D(256, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same'))
model.add(MaxPooling2D(pool_size=(2, 2), strides=(2,2)))
model.add(Conv2D(512, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same'))
model.add(Conv2D(512, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same'))
model.add(MaxPooling2D(pool_size=(2, 2), strides=(2,2)))
model.add(Conv2D(512, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same'))
model.add(Conv2D(512, kernel_size=(3, 3), strides=(1, 1), activation='relu', padding='same'))
model.add(MaxPooling2D(pool_size=(2, 2), strides=(2,2)))
model.add(Flatten())
model.add(Dense(4096, activation='relu'))
model.add(Dense(4096, activation='relu'))
model.add(Dense(1000, activation='relu'))
model.add(Dense(10, activation='softmax'))

# Model compilation

model.compile(loss='categorical_crossentropy', optimizer=optimizers.SGD(lr=0.001, momentum=0.9, nesterov=True, clipnorm=1.), metrics=['accuracy'])

# Model fitting

model.fit(x_train_, y_train_, epochs=1, batch_size=32)

# Model evaluation

score = model.evaluate(x_train_, y_train_)
print('Train loss after 1 epoch:', score[0])
print('Train accuracy after 1 epoch:', score[1]) 

I've tried normalizing the input, changing training sizes, increasing epochs, changing FC/filter size, and changing optimizers (and learning rate). Train accuracy is as low from both the evaluation report and TensorFlow's History report. I'm expecting >95% accuracy. What am I doing wrong?