Assuming this is a late registered Mk 4, there is only one relay feeding the mirrors(according to the workpoo manual (no did not spell it wrong), if it's a Mk 5 then don't know.
Possibility the switch is at fault. Tried to upload an image from the manual but 18.iKb doesn't permit !
With respect to the park assist suggestion 1 - remove battery negative lead for 10 minutes... 2- clean each sensor individually with soapy water ?