Office closing but no notice served?

Hi, I'm hoping someone can help me as I don't seem to be successful in getting accurate advice from my union rep currently and my company are not responding to any of my emails.
Last September, we were told that our office is closing down at the end of March 2019. My company has other offices around the country. I received an "at-risk" of redundancy notice in October and we started down the consultation route. Relocation was not offered as an option, although I would not have been able to take it anyway owing to my husband having children here, where we live. My current job was "advertised" on the Suitable Alternative Employment register, with a base location of home/hub - with the caveat that I would have to work from home permanently and after two years, the expectation was that the job would move to another office. Not being in a position to a) work from home permanently, or b) relocate to another office in two years time, I said that it was not feasible for me to apply for it and this was accepted. The consultation period was due to finish on 2nd Jan.
My directorate manager asked if I would be willing to consider a settlement agreement of an extra 6 months with redundancy at the end, to facilitate transfer of knowledge etc, with primarily a home base, but that he would rent an office space for two days a week, to enable me to fully carry out my job. I agreed to this, under the belief this would now take me through to September. The settlement was due to go before a panel on December 19th. I heard nothing. After Christmas, I emailed a few of my bosses, HR and the people running the reorganisation programme, but they were all either on annual leave or did not respond. January 2nd came and everyone in my office got their notice served, to finish at end of March, but I received nothing. Eventually, after the 5th time of emailing people (they're all based in head office and won't answer calls), I got a response saying the panel hadn't met, but that it would on the following Wednesday. Rinse and repeat every week until now. Every attempt made by myself to contact anyone involved in the reorganisation process resulted in total silence.
I contacted my union rep, who suggested that I could raise a formal grievance for failure to consult on the redundancy process (which I'm not sure is entirely accurate - they have consulted, just now stonewalling me), so I sent yet another email stating that I wanted a response within 5 working days or I would consider it failure to engage and consult and seek further advice. All I was told then was that the panel still hadn't met to discuss my settlement agreement.
Last night I arrived home to a letter in the post saying they have had to "extended my at-risk period". Nothing else - no dates, no indication of time frame etc.
My concern now is that I have a contractual 12 week notice period, so if I was served notice today, that would take me to 1st May. My office base closes on 29th March.
- Where am I supposed to work for the last 4 weeks of my notice? Can they force me to work from home?
- Can they refuse to serve me my notice, given that I'm being made redundant due to a close down of office, rather than my role being redundant?
I'm very nervous about all of this as I feel I am just being messed about to the point that they're trying to get me to resign, rather than face paying a (considerable) redundancy. On the grapevine, we have heard that the delays are due to the company not having enough money to pay all of the redundancies (some staff in head office had their voluntary redundancy pulled the day before they were due to leave).
Apologies for the lengthy post, but any help/advice would be very much appreciated. Many thanks.