Reaction of 2,3-dichlorobutanoate with a decarboxylating agent followed by hydrochloric acid and then aq. potassium hydroxide Question

$$\ce{CH3-CH(Cl)-CH(Cl)-COO- -&gt;[-CO2]A-&gt;[HCl]B-&gt;[aq KOH]C}$$ Product C is:
a) $\ce{CH3-CH2-CHO}$
b) $\ce{CH3-CH(OH)-CH2-CH2-OH}$
c) $\ce{CH3-CHO}$
d)$\ce{CH3-C(=O)-CH3}$

Answer

 The answer given is (a)

My attempt



Where did I go wrong?
Considering the follow up doubt, why geminal and not vicinal?

the carbocation formed is more stable because of $\ce{Cl}$ +M.