We are sorry to hear that you are unhappy with your wetsuit. However, we are unable to accept a return as the item has been used.
Although temperature is subjective for all people and the activity they are undertaking - personally for instance at present in the UK when surfing or foiling I am in a 3/2mm suit, brands do give temperature guides for wetsuits. While we do not list a temperature guide for the suit on the page you purchased from - https://www.thesupco.com/wetsuits-c6/ion-womens-element-semidry-wetsuit-5-4-front-zip-p4698 - ION do give a temperature range for this item on their website for this model - https://www.ion-products.com/en/uk/products/ion-women-wetsuit-element-5-4-front-zip-2023-48213-4540?variant=42009375899787. The range given is 9°C - 14°C 48°F - 57°F. A 5/4 wetsuit is commonly referred to as a winter wetsuit for watersports, so I am very suprised to hear that you are cold even when swimming at the surface in water termpatures that are 17 degrees, but of course temperatures are subjective.
Scuba Dvier Magazine give the temperature range for a wetsuit of 5mm below. They also point out that wetsuits vary for different sporting pursuits https://www.scubadivermag.com/wetsuit-thickness-and-temperature-guide/
62.6°F – 69.8°F / 17°C-21°C 5mm full suit
The globally recognised diving organisation PADI go on to highlight this difference in wetsuits further - https://blog.padi.com/differences-between-surfing-and-scuba-diving-wetsuits/ As such ION do not manufacture diving wetsuits but rather wetsuits for a broad range of 'surface' watersports such as surifng, kitesurfing, windsurfing which compliments what we offer.
I hope you find the information above helpful but we are unable to accept your return due to it being used. You'll find more information about Returns on our website here - https://www.thesupco.com/returns-i21
Please let us know if you have any other questions.