Dear Andrea, first of all let me thank you for having shared your feedback with us. The important thing is that you had the chance to experience two amazing sites as Pompeii and the Vesuvius.
Regarding this latter, unfortunately the guiding service on the Vesuvius doesn't depend on us: the guides are Vesuvius National Park employees and the service they offer is not that good (as you mentioned, it happens that they simply walk off and don't care about the visitors they should escort!). Any company you use, this part of the visit will work the same way.
The issue with the bus... what to say: we are REALLY sorry. Unfortunately things happen. We did the possible and impossible to provide a new bus the fastest we can, and thanks to that the tour could go on with almost no more hussle (well, the air conditioned may look like a big isse, but in mid May generally noone uses it yet :-)))) )
Thank you again!