Key fob not working

Hi I have a 59 plate c220 and noticed yesterday that the unlock button on the key fob no longer unlocks the car and I had to use the key to gain access every time,the lock and trunk buttons do still work ok as do all the buttons on my spare key.

it was working perfectly fine on Saturday with no problems 

ive changed the battery but it still doesn’t work has any body came across this and what may be the problem 

thanks in advance