Hi and welcome to the site .Does the modem go off at the same time of the day or is it a different times.2 Does your next door neighbour or any one in the street having the same problems.Not every one phones in a fault so there may be more of you

Make a log of when it goes off and this could be passed on so they can monitor when yuor modem drops out.This has been done in my aera as we could not find a fault when we arrived .