Perhaps there was a misunderstanding and they thought you were going to quit? To be honest it sounds like there is now bad blood between you and the employer and they are trying to get rid of you (illegally) because of that. They can't force you to resign if you are prepared to work full time as per your contract.
Unfortunately i think they are justified in asking you to work full time as per your contract. Im all for flexible conditions and looking after the kiddies ... Where the employer can accommodate. Employers have Needs too and it's not their fault your husbands job changed drastically (Did your husband have a choice in taking on this new job?).
It must be a horrible feeling, having to walk into the office right now. Best of luck and I hope this gets sorted soon for you..