Booked a reservation that was confirmed only to find out there are no seats available

I cannot stress strongly enough how disappointed I am in the help with my seating problems.  I DID NOT want the company to do what they did with the request to the airlines and now I run the chance of being bumped and not being able to make the connecting flight, which will completely upset our plans for our long awaited for vacation.  I will not use this company ever in the future to book flights and will tell everyone I know how they do business.  On top of it all, when I called to clear this up, I waited for a half an hour on hold and then got someone who had such a strong accent that I couldn't hardly understand what they were saying.  I did get that he said I definitely had a confirmed reservation and would not be on standby which is completely wrong, I learned after calling the airline (and this is on top of making my reservation more than 10 days in advance).  Their customer service is totally unsatisfactory.