Do not accept a month notice according to them the today the 1st is not a month, can only cancel the 1/5/2023

When I want to give a month notice for today the system only aloud me to give month notice from the 1 April? please explain that? it is today the 1st it is a month notice? You increase the line speed as you like increase the package. I'm not interested the other supplier give the same line speed currently and give me a better price.