In addition to talking to your UCU rep, there are a number of things you can do that will help to resolve problems at work.
Firstly try to resolve the problem informally on a one-to-one basis directly with the person who is causing you the problem, if you have not done that, and you decide to make a formal complaint, the complaint may be dismissed.
If that fails to resolve the problem, or if the lack of communication with that person is the problem itself, take the issue, still informally, to your appraiser or line manager (unless that is the same person against whom you have the complaint), seeking to settle the issue amicably and productively.
If the problem is not unique to you, and is shared by others in your department or subject group, then you are advised to try to resolve it collectively, as a collective issue may more easily be settled long-term than an individual problem. It may be that this is the point where, logistically, you are best advised to approach the UCU rep, asking him/her to 'chair' the informal gathering of affected staff and give advice as appropriate.
Throughout this process of informal attempts, build up a record of the process - of the problem and of the attempts to resolve it informally - listing dates of memos, meetings, events, incidents, etc and keeping whatever evidence may be relevant.
If the problem is still unresolved by informal approaches, then go to your UCU rep. Only if your rep cannot resolve the problem, or if advice is sought, will the next stage in the process be activated by the rep, ie referral upwards through the union's system.
If you are called for a disciplinary hearing, you should of course contact your UCU rep immediately and should make no attempt to resolve the issue informally after that.