Hi nana2b
Unfortunately, people don't like being complained about, so there is no way of going about raising this where I can guarantee that the social worker won't 'get their back up'. One would hope that people would be mature enough to accept that when an issue is raised they might have to look again at the way they go about things, but sadly this isn't always the case. On the other hand, the social worker may not be being deliberately rude in not speaking to you, but simply thoughtless because they are extremely busy with other cases. If it is drawn to their attention that they are apparently ignoring you, they may want to rectify the matter by giving you some time and attention.
Having said that, if you do decide to raise the matter, if you are concerned about consequences then you could pay particular attention to how you word it when you do so, and make sure it doesn't look as though the social worker is being personally attacked.
You could start by trying to have a quiet word with their manager, or with someone else who could speak to the social worker, for example the Independent Reviewing Officer if the child is looked after.
The most direct way of approaching it would be to make a formal complaint, and if the social worker's behaviour towards you persists you should certainly think about doing this. However, it could be best to try less formal ways first. Our advice sheet 25 takes you through the procedures for making formal complaints:
http://www.frg.org.uk/need-help-or-advice/advice-sheets
I am going to ask for the name of the local authority to be removed from your post, as my advice would be the same wherever you lived. This forum can be read by people not actually posting here, and it is best to keep your posts as anonymous as possible.