Sorry I don't know what OEM means but they were fitted by my local MB dealer. The front sensors are definitely active at low speeds and as I said they do "sometimes" beep when I brake. I am going to phone the garage but I wanted to check beforehand to see if they should have installed a switch for me to be able to disable them if needed, As I said being in a traffic jam is hell.
Can you clarify, is the traffic jam an issue because you have to brake and that makes your parktronik beep or are you driving too close to the next car?
This is the switch you should have if the system is MB original (=OEM). But you should not need the switch at a traffic jam. Make them fix their installation.
(Edited: this one is actually for a W211, for some odd reason I picked up the the W211 even if you seem to have a C-class car, but this should be similar, the button may be elsewhere).
Indicator lamp If indicator lamp
is on, Parktronic is deactivated.