I'll bet that the electrical panel was probably installed before the refrigerator was put in place and there may not be enough slack in the wiring to pull it forward to access the area.
You might try using an inspection mirror and flashlight or a flexible camera scope to see if you can cut the paneling away from between the water heater compartment and the space under the fridge and without cutting any framing supporting the fridge and cabinet wall. That might open up things enough to access the area. Also using a flexible camera might allow you to see if the wiring has enough Slack in order to pull the electrical panel forward.
If you cut the paneling away, when done you can either leave it open or make a cover panel with a few screws to close it back up.