Broken torsion spring

I have a 16 by 7 aluminum garage door, at least I believe it to be aluminum its a model 6RSTW. Several years ago one spring broke after more than 10 years. I called out a this guy that replaced both. A few years later one broke. He came back out under warranty and replaced the broken one. Today one broke again. (he is not allowed back to my home ) Here is my problem. The original springs are gone and I can only reference what he installed which I believe are smaller than the originals. I say this because I can see where the original screw marks are on the bar and these appear weaker/smaller than the originals.  Clearly he installed either refurbished or cheap ones. How do I find out what the originals were.... I am afraid to call a company out fearing they will simply match replacements up to whats there. I assumed it would be a simple issue to just give the size if the door and the construction type to get the proper springs but I am only seeing references to matching what I have. Please advise.

Did the door balance with the springs he used? Was it easy to open & close manually? If so then he may have used a lighter gauge spring wire. This isn't necessarily bad it's just that the springs wouldn't have as many cycles has heavier gauge springs. A cycle is one open/close of the garage door. A typical garage door will come from the factory with 10,000 cycle springs (but I've seen manufacturers use 8,000 or even 6,000 to cut down on costs).

If your door worked up & down fine with the springs he used then I would suggest that you tell whoever you get to replace the springs that you would like high cycle springs. They could calculate the new springs off of your existing springs. They would typically go up 1 or 2 wire sizes depending on how many cycles you wanted (and how much room you have for the longer springs). Going up to 20,000 to 30,000 cycle springs should be fine. Of course the bigger they get the more they're going to cost.

Hope this helps.

I replaced torsion springs on my garage door several years ago after one broke. It was a DIY project and it went well.  Upon researching both the physics and the lore considerably, I found that purchasing replacement springs from a reliable internet supplier was the way to go -- both for cost and selection.  There are several and their websites are quite helpful.   Here are some suggestions whether you DIY or "team" with a repairman.
1. Weigh the door in the "down" position.  Easily done by placing it in "manual" mode, i.e., by disconnecting it from the chain drive assembly.  Most units have a pull cord for doing this.  Place a bathroom scale under the middle of the door and jiggle the scale with your foot a few times.  Repeat to obtain an average.  (You can get fancier if you wish and calibrate the scale when you are done by climbing on and off it while holding a known weight near that of the door.) 
2. Measure the opening height of the door (floor to the horizontal tracks will do). 
Foregoing provides information needed to order springs.  Always replace in pairs since 8-10 yrs is nominal lifetime for them and you want them to be matched so the door is balanced properly.
After installation, an easy way to assure that the springs are "right for your door" and installed properly is, with the door disconnected from the drive and approximately halfway open, to confirm that it takes little or no hand force to keep it from moving up or down.  With a little push in the up direction, the door should rise; similarly for the down direction.