I am sorry to hear this and for any inconvenience this may cause.
We would recommend checking the network in your area here and if it is looking all clear please can you try;
-Rebooting the handset.
-Turn aeroplane mode on and off.
-Try your sim in alternative phone.
We do have a coverage checker that will show you what coverage to expect with us specifically, but @Strat is correct in saying we run on the EE network and any outages or maintenance will show on their network checker.
Just for future Information if you go to the EE support pages and given them your PlusNet number EE will keep you posted on the phone mast you report via Post Code to check for service.
I did this last year when my local mast went off air and just the week before last it went off again and I had an SMS from EE telling me of the problem then another SMS hours later saying they can’t fixed the problem remotly and an engineer needs to go to site to fix it. Next day had another SMS saying it had been fixed and sure enough it had.
Never had anything like that from other providers with them being up front with the problem though the Three network uses the same cell but don’t send text’s of the problem but they do sometimes flag up any problem on there support pages.