To verify if your transducer is still working, remove it from inside the hull, dangle it in the water, and see if you begin getting accurate readings again. If so, you can remount the transducer.
One other thing to consider is the material in the hull of your kayak. I checked out the Elie Coast website, which describes the hull material as "Used in all Elie kayaks, three-layer Poly-XR™ material is 30% more rigid than standard polyethylene, thanks to an advanced resin in the top layer." It is possible that the three-layered construction is interfering with your transducer signal. I recall that boats like Boston Whalers that have a foam core between fiberglass layers cannot use through-the-hull transducer mounting because the foam layer interferes with the signal.
If you try an inside the hull mounting again, use Duct Seal putty rather than Goop. That is easy to reposition or remove.
Native Watercraft Manta Ray 11 and Slayer Propel 10
Member - Pro Staff team for Native Watercraft
Author - "Fishing in the Comfort Zone" - light tackle fishing techniques for kayaks and small boats