XC100 data readings constantly wrong - and customer support not responding?

I’ve had the Rally XC100 pedals since December. Installed them as per instructions. First faulty readings started appearing within days. Logged a support request with Garmin who went through a lengthy (and often repetitive) troubleshooting sequence. The pedals work ok for maybe 10 mins and then the data starts reading off (really low). Calibration and reinstalling fixes this occasionally for maybe another 10mins.

Are Garmin pedals really this bad? I sent a request for support on Monday, but no one is replying. Garmin customer support are so bad - with Assioma, I had a response within hours! 

Has anyone been able to get in touch with Garmin UK recently or are they trying to fob me off? Considering raising a formal complaint next week and then try claiming through my credit card company as these pedals are garbage and I have an event coming up. I hope no one else gets them and goes with Assioma instead!!!