Sorry OP, I haven't read the whole thread, but my first move would be to call the LL and tell him you think there's been some sort of problem with the bank, and you are going to call them to find out what's happened, and will get back to him as soon as possible. This will show him that you're about to become pro-active. As soon as you've done this, then check exactly what date the rent stopped being paid, and call your bank to find out why. Did you cancel the Standing Order? Have the bank themselves made an error? Presumably one of these must have happened, if you've been paying for 3 1/2 years by Standing Order without any problems. Once you've spoken to the bank, you will know if the error is yours, at that point, if it is your fault, I would ring the person who was kind enough to agree to be your Guarantor, and explain to them what has happened. Clearly you need to grovel if it's been your mistake, but I would then ask them if they would be in a position to lend you the money, so that you can immediately pay your LL what you owe him. If they are, then call your LL back and tell him when the Guarantor has said they can pay, that will get him off your back. If however the Guarantor has said they don't have a lump sum to pay, then you need to talk to the LL, be completely honest with him, and ask him to give you a couple of days to see if you can borrow the money from someone else, but whatever you do, do not avoid the LL, or tell him ANY lies, as the minute you're dishonest with him, you're going to give him a reason to set the wheels in motion to evict you. Sadly, this situation, assuming it is of your making, is going to leave your Guarantor in the crap, as one way or another they are going to have to find the money, as they've signed a legal document agreeing to do this.
Once you’ve got the rent situation resolved, I would then make an appointment to see someone at Citizen’s Advice, to see if they can help you resolve all the other bills that you haven’t paid.
This all assumes of course that this story is true in the first place??