If you were paying through Apple, see Apple support's articles below:
If you want to cancel a subscription from Apple – Apple Support
and
If the subscription that you want to cancel is not listed – Apple Support
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Or if you were not paying through Apple:
From the color widgets website ...
https://mmappsinc.com
Their terms and conditions :
https://mmappsinc.com/terms
say:
"You can manage your subscriptions and turn off auto-renewal by going to your Account Settings in the iTunes store after purchase. Any unused portion of a free trial period, if offered, will be forfeited if you purchase a subscription to that publication, where applicable".
If this doesn't work for you, you could go to the website (link is above), to contact them, or get support.
All the best :-)