Unfortunately there have been instances where disabled people have been over charged for the same journey as a abled body person and is probably more widespread than we would like to think but still a minority of drivers and companies.
Most taxi cab drivers we have encountered have been great will help load my wifes folding wheel chair etc if required even if the vehicle is not a designated accesable taxi.
The crux is you cannot by law charge a disabled person more for the same journey as an able bodied person, the equality act of 2010 expects drivers of PHV especially those designated to carry out reasonable adjustments for disabled users such as opening the door, helping to fold down wheelchairs and storing them, placing the ramps and securing the wheelchair etc etc.
In reality the extra time it takes to any of these things is marginal and shouldn’t be used to stiff the disabled.