Just spent 1/2 hours talking to a guy in India, he said " the router in new and it has to settle down,
so give it until Saturday to see what happens, then call me back .....Bye.
I think there is a saying "don't pi$$ up my back and tell me it's raining"
I totally get the situation my broadband went down for a week recently and I hadnt realised actually how much Id treated it as basically an essential service now, and yet no amount of pestering the phone company responsible seemed to make them treat it as a priority for a fix, and it was hell for me
but your guy in India is just reading a script, and technically he is right, your broadband was running slow for a while because the automatic systems behind it were seeing packet loss, ie errors for whatever reason, so it kept stepping down the speed till it felt it was providing you with a stable speed connection with the least amount of errors.
Just replacing the box in your home doesnt instantly fix that. these automated systems have to spend time learning your connection is now more stable at higher speeds again, before they apply the new higher speed profile and that can take days or maybe even a week before that process kicks off or is completed.