The e-mail stated: "Your home in the sun for just £22.49 a month – less than your holiday! And own your property abroad for less than your holiday."
A recipient challenged the claim for being misleading as she understood that buyers bought a two-week slot for 15 years, after which the property was sold.
She also felt the ad exaggerated the profit available to buyers when the property sold.
Home Shared Ownership responded on behalf of Matalan and itself.
It said if the ad was found to be in breach of the CAP Code, it would make the necessary amendments in future advertising.
The ad stated that property prices could rise and fall depending on market conditions. Historically, though, property would always go up in value.
Although the advertiser had provided data that showed the historical position on which its claims were based, the watchdog considered it was not sufficient to guarantee that profits would follow the historical pattern.
It therefore concluded the claims were misleading. The ad must not appear again in its current form.