2013 A6 Avant Wheel Speed Sensor Issue

I'm having a spot of bother...

It started in November when the dash lit up with various warnings about ABS, Auto Handbrake, TPMS etc. I scanned the car with Delphi and it showed three errors relating to the front left wheel speed sensor, bought one off Amazon, fitted it and had no problems till last week when the same lights came on the dash, scanned again and it showed the same three errors but relating to the front right whell speed sensor, i thought it a bit odd but i ordered one from the same seller on Amazon, fitted it but the lights remained on, drove through town to fill up, then upon restarting the car the lights were off and the car was back to normal, happy days. However, next day after i went away to work my wife told they came back on again. Told her to take it to a mate in Kwik Fit, he swapped the sensor again, no change, suggested it was the Wheel Bearing, swapped it, no change, he thinks it may be a wiring fault? Anyone had anything like this before?