... should be MikroTik?
Probably, there's a MikroTik company in Latvia that makes routers and wireless ISP systems.
In American countries where Telefonica/Movistar operates and sells broadband service, they use ADSL/VDSL modems made by Wu-Xi Mitrastar Technology Corp. under the MitraStar brand, probably also rebranded and sold under other names.
Indeed, the telco retains access to do things like ...
Well, to do things which you have no knowledge about or control over.
You can secure access to the unit through a strong PW but you cannot change the name of the admin: field so there goes the imaginary security you thought you could have had and there does not seem to be a source of firmware files to upgrade yourself.