ios 11.2.6 old voice control not working with bluetooth devices

I just bought an Iphone 6s 32 gb with Ios version is 11.2.6.

I discovered that the old voice control does not work with my Bluetooth car stereo, a Sony, mex-n4100bt, and

also with any other of my Bluetooth devices.

When i switch to siri mode, the voice control is working fine with all my Bluetooth devices.

With my old iphone 5, ios 10.3.3 everything worked fine and i was very happy.

My big issue is that Siri is not available at my Language, Greek and it is a matter of safety during driving, while with my old iphone 5 i use a lot the voice control to make calls from my contacts and now it is not possible.

Kindly inform me what's the problem and if Apple is going to do something about it.

Many thanks in advance