Sadly this is such a common occurence and happens over and over again. There are many ' mow & blow' merchants out there who will cut your grass and hedges, but have no knowledge of plant identification, species or seasonal pruning techniques, plant care or anything else. A van, a mower and a hedgetrimmer do not a 'gardener' make!
Skilled, artisan craft gardeners are a 'rara avis' and are a rare commodity amongst the hordes of so called 'gardeners' out there in the land of self employed mobile gardeners. To garden properly takes time and skill - the concomitant affect being that hourly rates or price for a job would be high, akin to that of any other skilled tradesperson, and rightly so. This is the reason I am not prepared to be a self employed gardener - it is doubtful if I would find much work as for some reason clients expect gardeners to come cheap. Factor in elements such as the cost of disposal of 'arisings', travelling time, maintenance or replacement of expensive machinery in addition to income tax, national insurance, pension etc and it gets expensive!
I am also angry on your behalf OP, but angry also that this kind of behaviour leads to all gardeners having a bad reputation.
Not much help to you in this situation, but for future reference, if you are going to engage a gardener, either as a 'one off' or on a regular basis a few pointers:
Ask to see a portfolio of their previous work - a skilled gardener should be proud to showcase what they have achieved previously.
Walk around with them and try to gauge their knowledge of species identification - if you ask for a particular shrub, tree, bush or plant to be pruned they should advise whether or not it is the correct season to do so and warn you of the possible consequences if you insist on it being done out of season.
Ask to see evidence of Public Liability Insurance - it is common for strimmers especially to throw stones at high speed, broken windows, car windscreens etc are not uncommon.
Ensure that they have a Waste Transfer Licence to legally transport and dispose of 'arisings' - as the instructing person you can be vicariously liable for any unlawful or innappropriate disposal.
Check their attitude to health & safety - appropriate safety clothing should be worn at all times - it horrifies me that anyone can go out and buy a chainsaw, ( one of the most dangerous tools ever invented), with no training or experience and start weilding the thing about with gay abandon. I have seen people using them wearing just shorts and nothing else - no ballistic wear, safety boots or proper forestry helmet. The same applies to strimmers, blowers and hedgetrimmers, all capable of causing fatal or life changing injuries.
Check their attitude to wildlife - no real gardener would willingly destroy any valuable habitat at the wrong time of year, ie nobody should be cutting hedges from March to August during bird nesting season and they should advise you accordingly. A gardener who loves plants is almost certain to have an affinity fir all other forms of wildlife too - it will tell you a good deal about their attitude.
Once again I am so sorry to hear that this has happened to you - hindsight is a wonderful thing!