If you use free internet there will be very slow speed of internet because of it is free like you many are using so the internet speed gets slow. Using of free internet causes your phone or pc Daisy’s also because the network which sent by the modem will be lack of virus when the owner keeps any security wall to the network.
And there are stations and airports with the free WiFi network of will be slow and you will rid from that slow speed network.
If you are getting slow speed of your own modem then you must have been finished your data or may be there will be some technical issues in the company.