Loads of conflicting advice for you here - I'm hesitant to join it but here's my view
Firstly you have been treated appallingly with no consideration for you as a person
However.... legally, the employer has probably done nothing wrong if they can show they complied with their own written protocols on handling this. They have 'evidence' and have to investigate
If you go straight to the legal route I'd consider what you are hoping to achieve. Is it to retain your job? Sue them for constructive dismissal?
30mins free advice will give you chance to hear an opinion. 30mins goes very quickly. Go in with everything clearly and concise ly written. e.g. I have been employed for x yrs on a permanenet contract.
Keep records of every phone conversation (date and time them) and also letters and keep your records in order.
I would pursue the unison route and exhaust that mean time. If your rep is either unsympathetic/over worked or just not 'up to the job' ask to have another one.
In black and white on paper it may break down to
They had clear evidence of fraud
It amounted to something which would substantiate instant suspension
They did ...following procedure
You were kept informed of when you would be seen and they delayed a week in order that you had your leave uninterrupted
Take out your experience of it and it sounds more reasonable. (I know it's not)
Next bit is crucial.
You do need to answer the allegations. You don't need to answer in detail if you have nothing to offer - someone said a straight answer of not my machine/not my working day should be tagged against a lot of them - take those events out of your equation.
Next question. Do you share your log in details - that is probably an offence?
Remember what you can and offer that up with a covering note to say that the evidence on the roster was (you assumed) accurate but it would appear to be tampered with or corrupt. It is not down to you.
I personally think being off sick is good - you need that space, the employer has to acknowlegde outcome on you, in a subsequent court case you have evidence of effect on you
I sound unsympathetic -I'm not (see line two) I'm just trying to be constructive :)