Well if they didn't look at it, there's the problem. That is such a basic mistake, unless it's the sort of company who charges double what you paid so as to cover all eventualities.
For what it's worth, a lot of successful domestic cleaning companies simply will not touch anything that is as dirty as you have described, as it's just not worth it for them. It needs a company that specialises in one-off cleaning of empty homes, student lets, etc, and you'll pay accordingly.
Also, you say a company sent a cleaner, well if it really was a company (as opposed to an agency) then £20 per hour is nowhere near enough to have charged you, if it is they are going to pay the staff properly and make a profit from it.
I have done deep-cleaning in the past, many times, and I detest it. I have only done it to help people out - it's a filthy, horrible job and there's often no end in sight. I much prefer regular visits, with a concentrated effort on one area each time, to get the place in order, but it does take weeks before the whole house looks clean, assuming I go weekly. Also, I do not and never have charged by the our. I agree a price for each visit and stick to it. People pay me for the outcome not the time. Question is, do you feel you had £80 worth of cleaning?