2 plot diagrams appear when only creating 1

Question

I'm trying to plot a data frame in a line graph and customise the labels, title, etc. However, it seems to create an empty diagram instead.

plot_df= plt.plot(df)

plt.figure(figsize=(30,8))
plt.title("TITLE.", fontsize=24)

plt.xticks(rotation=30, horizontalalignment="center", fontsize=16)
plt.yticks(fontsize=16)

plt.xlabel("X", fontsize=21, labelpad=12)
plt.ylabel("Y", fontsize=21, labelpad=8)
display(plot_df)

Said diagrams:

So the question here is, how do I customise the intended plot without conjuring up an empty one?