Employs of mtnl are not doing their job

I am using their internet for like 2 years now .Today I called mtnl to submit a request to change my normal modem to a wifi modem and what they said is that I dont use their internet ... the next time I called for the same issue and what they say this time is I dont use their modem... their service is poor. They make a simple task like changing a modem look like its building a tower. The people sitting in the help centers are not willing to help and they are rude. I cant waste my whole day to call them for this. I have used other company's internet and I am still using , I have faced no problem in their service, but mtnl kills my time !! my modem no : 410tc1 provided by mtnl.