Helen Armstrong, 35, relies on oxygen 24 hours a day because of her severe asthma and a hole in her heart.
But she has not been getting her vital oxygen cylinders since private company Allied Respiratory took over the contract from local pharmacies in February.
Even though Mrs Armstrong applied to the firm for supplies at that time none has arrived, despite constant phone calls from Mrs Armstrong and husband Tom, 41.
She has been able to continue picking up small supplies of oxygen from her pharmacist, as she did before the system was privatised.
But this is being phased out and she is dreading the day when she has to rely on the company for supplies.
Mrs Armstrong, of Martin Road, Leigh Park, said: 'I don't understand why the system has been changed and they have stopped something that was working very well for everybody.
Allied Respiratory general manager Tom Temple refused to speak to The News, but an NHS spokesman admitted there had been problems with the supply.
He said there had been a backlog in supplies as a result of 'a huge surge in demand' after the new system started.
jenny.haworth@thenews.co.uk