Signia Stretta phone call problem

For context I’ve worn hearing aids for over 40 years so I’m quite well versed with them. However I’m really struggling to sort out a technical issue with my mums hearing aids. She was given some Signia Stretta RIC hearing aids from the NHS and has the signia app on her phone.

She is able to use them for everything including streaming music and videos etc but she is unable to make or receive calls as the person on the phone cannot hear her. She can hear them perfectly. Even if she receives a call and tries to take out her hearing aids/turn them off during the call it doesn’t work.

it’s as if the microphone is totally blocked once the Bluetooth of the hearing aids is enabled. I went with her to see the audiologist who was completely dismissive and said they couldn’t do anything and to contact Signia. When we contacted Signia they said we had to go back to the audiologist but as it’s NHS we don’t have the same support as if we bought them.

I’ve gone through all the settings on her iPhone, the hearing aids are paired correctly. There’s nothing I can chance in the Signia app. Is this a fault of the hearing aids or should something have been enabled upon the initial installation?

Thanks in Advance