I think "promontoría" has got to be a typo for "promotoría". "Promotoría" can refer to a number of different kinds of agency in different contexts, and there's really no telling which sort it is here. I would put just "agency". It probably refers to some sort of agency representing the company in some way. I presume it means that notice was not properly served because it was not delivered directly to the company itself but to an agency providing some sort of service to the company or representing or promoting it in some way.