TWT - Where are my Tyre Sensors ? TPMS

I went to Tiger Wheel & Tyre Durbanville to get my tyres checked(End of November 2017). After inspection i was advised to replace them, naturally i decided to replace all four tyres.

Service was good and i was kept up to date , had to do an alignment as well which was a bit of a concern for me however i was shown it was necessary.

However , my car has a Tyre Pressure Monitor System which means each wheel has a sensor connected to the valve. I noticed that my valves were changed as well, i guess this is TWT procedure, but up until recently checking my tires its confirmed that the sensors are no longer on my wheels.

Now why would the Tech replace my valves and not mention to me or anyone for that matter that my sensors are being taken off? (sensors are connected to the stem of the valve in the inside of the wheel) I am inclined to think perhaps they broke it or where not aware of it ? - TWT did make me fill in a form stating what marks are on my car ,etc but no mention of a TPMS. Ofcause i entrusted them thinking they are professionals and know about the necessary technology concerning cars and essentially wheels.

Bare in mind i had them fill my tires with nitrogen which is why i was not too concerned about NOT receiving any TPMS notifications on my dashboard for a short while. Now i have a system which cant fulfill its purpose due to a Tech at TWT durbanville which either did not know about the sensor or broke it regardless they did not mention anything to me! Those sensors are not cheap but yet they failed to mention anything to me the customer.