Rights Of Disabled Persons and the Bangladesh Aviation Industry

In Bangladesh a number of local airlines sprung up in the past decade. They are not to be compared with the budget airlines of other countries because they are not cheap. They are just balancing the supply side of a growing demand of local aviation industry. The state carrier Biman's inability to cater the market has further strengthen their position.
But that does not mean that there is enough competition to stress on making the service better. One such example is that how they treat the disabled passengers. A paraplegic and a wheelchair user wanted to book a flight in Regent Airways from Chittagong to Dhaka. They refused the booking saying that they do not have lifts to carry a wheelchair passenger to the Dash -8 aircraft, he/she has to climb the stairs. This is a direct turnaround from what they advertise on their web page:

At every airport REGENT airways may provide wheelchair facilities for the disabled passengers or customers who cannot climb stairs.

A mechanical lift. Image courtesy Adaptive Engineering

The international law says carriers are required to provide boarding assistance to passengers with disabilities by providing a mechanical lift or other device. The citizen charter of CAAB also ensures the rights of the disabled people.
The sister of the passenger posted the complaint in Regent's Facebook page and she got a reply with an apology. The message also says that they were unable to provide the service as as they don't have the required mechanical lift. Biman, the major Ground Support Equipment [GSE] provider at all Bangladeshi Airports, also does not have any passenger lift car suitable for small aircraft such as the Dash-8.
Now my question is there are other airlines like United Airways who use Dash - 8 aircrafts in Bangladesh airports. Was it too hard or expensive to buy mechanical lifts for all the airports. And how did they get the license without securing these basic requirements in the first place? I think its time somebody should sue them all to get the basic rights.