Ridge vent conversion creating heat problem
This is a horrible problem to have, and yet you will encounter many who will insinuate that you are crazy for suggesting it. Hold strong: you are not crazy. The problem is real. More insulation is not always better in all situations for all climates at all times of year irrespective of ventilation. Ignore people who claim this. They have never personally experienced this phenomenon, as you and I have.

Here's what's happening: The added insulation is indeed slowing down the heat transfer, so less heat is entering your house during the day. However, the amount of diminished heat transfer may be a lot less than the sticker R-value might suggest due to a multitude of factors, and poor design or installation choices made during the work may actually have resulted in more heat gain. Here are some options for you to investigate:


Attic ceiling not air sealed; hot attic air can go right through the insulation and into the house
Uneven insulation application; heat movement barely diminished in some areas
Scammy contractors didn't blow/add as much insulation as you paid for; R-40 attic floor insulation is about 11" deep if it's all cellulose and 15" deep for fiberglass. If it's shallower than that, you got robbed!
Use of fiberglass, especially on the top layer; fiberglass is more air-permeable than cellulose, and slightly IR-translucent, which means the the infrared heat transfer from the roof decking is not getting blocked as well as you might expect
Potentially darker roofing material dramatically increases the amount of heat that the attic receives throughout the day
You said they "replac[ed] the original venting with ridge vent." What was there before? Gable vents? Turtle vents? This matters, because if you live in a windy area and/or if your roof has a low pitch, then turtle or gable exhaust vents may be more effective than ridge exhaust vents
Contractors might have clogged the soffit vents, and if there are only a few of them, then they may not be sufficient to provide enough air for the new ridge vent
The house now cools off less at night because of the insulation slowing down heat transfer out of the house once the attic cools down to below the indoor temperature; the insulation is working against you after the sun goes down!


So, what do you do? Here are some options, presented in ascending order of cost and hassle:


Once the sun goes down, open the windows and turn on your bath fan to cool the house
Ensure that soffit vents are unblocked
Ensure that the ridge vent was installed properly and is not blocked by anything
If the insulation is uneven or lumpy, smooth it out
Add more soffit vents
Add a solar-powered attic ventilator, and face the solar panel west if at all possible. Western sunlight is your enemy; use it to your advantage by having it power a fan to exhaust the hot attic air (note: only do this once you have air-sealed your ceiling/attic floor)
Add gable vents (if applicable)
Staple a radiant barrier under the rafters
If the top layer of insulation is fiberglass, add a few inches of cellulose insulation over the top of it
Lay a multi-layered radiant barrier OVER the insulation on the floor (note: must be multi-layered, such as http://insulmation.stores.yahoo.net/thcome.html (no affiliation), since the top will get dusty so there must be additional layers that dust will not settle on)
Add a whole-house attic fan and run it as soon as the sun goes down (note: only applicable in a dry, mountainous climate, and make sure it has insulated doors that are closed during the day)
Replace the roofing material with something lighter-colored and preferably made out of metal, installed over ridge-to-eave purlins to create over-sheathing ventilation channels