Welcome to aviation! Most companies receive applications every day and simply do not have the resources, time and/or inclination to reply.
There are plenty of posts on this forum on strategies of how to get a job, I suggest you get searching. It is certainly worthwhile joining the IPA:
www.ipapilot.com as they (in my experience) are better geared to help people get a foot on the ladder than BALPA who seem to be more effective for pilots with experience.
With your hours, you need commercial time and there are plenty of opportunities out there such as instructing, aerial photography, ferry work, air taxy work etc... Many of the operators you have targetted will look upon you more favourably with 1000hrs in your logbook. Also look at
www.ppjn.com
I hope you didn't fall for the sales hype from your training provider "The market is bouyant, there are plenty of jobs etc..." If necessary, take any job that is connected with aviation (ground handler, check in, dispatch, operations assistant) as this allows you to make useful contacts and shows plenty of perserverence for the old CV.
It won't be easy but you'll get there in the end and believe me there hasn't been a single day when I don't feel lucky to do this job!
Good luck.