That's so annoying when someone calls (especially 'officialdom,') and they don't say what they want. So you worry. 
When we rented privately a number of years ago, the property agent left an answerphone message saying 'please can you call with regard to your rent we have not received.' We started to panic and wondered why, as it HAD gone out of our account the previous day. It pissed me off though, because it was 4.50pm on a Friday and I missed the call as I was in the garden. I rang back (within 10 minutes of them calling,) and the answerphone was on and they were shut down til Monday.
So we worried all night, and all weekend, and then when we finally got through on the Monday, the manager said that 5 minutes after leaving the message, he discovered he had made a mistake, and it HAD come through!
Why the fuck he could not have rang back 5 minutes later and left me a message saying all was OK is beyond me. Really pissed me off. Especially as he had rang a couple of times before (several months back,) and said 'can you ring back please?' with NO clue as to what it was about. (Also on late afternoon on a Friday!) I was so pissed off after the last occurrence, that I deactivated the answerphone, so he could leave no more messages and would have to keep ringing til I answered.
I am sure it is nothing serious OP, as if it were, you would probably have had a visit. Can't advise you fully, as I don't know enough about you sorry, (like if you're on benefits etc...)
Don't worry (easy to say I know!) and try and put it out of your head til Monday. (Some council offices are open Saturday morning BTW, so you could try and get through tomorrow...)