I agree with squiffy - you need to get a lawyer.
I join the queue of posters who are utterly confused as to the actual allegations. Is it flexi fraud, or internet misuse? Or both? Has any cognisance been taken of your explanations that you were off on certain days / didn't use specific computers? There seem to be massive gaps regarding the integrity of evidence,especially IT records.
Were the allegations relating to internet misuse raised during the investigation meeting, or are they new allegations, which you haven't had an opportunity to respond to?
The witness statements from ubercow - when are they dated? Is it before or after the investigation meeting? Was she one of the ones texting you? If so, this is highly relevant, as a key witness was making inappropriate contact with you during an investigation. (well done btw, for restraining yourself about contact during this time). You need to get on record that you believe these are malicious and unfounded allegations by this individual, driven by her dysfunctional relationships in the workplace, as can be evidenced by other staff.
You need to get your other colleague to provide a statement, if she hasn't already - both to support your timekeeping and also the difficulties with this other individual. Can she dispute the allegations? What about the member of the other team who you say you were cringing about when ubercow was really rude to her? Can she provide evidence? You need to start slinging mud to defend yourself.
Having said that, the burden of proof lies with your employer, not you, albeit that they are proving on the balance of probabilities, not beyond all reasonable doubt.
These are questions / tactics that come to mind, but as Squiffy says, don't try to address them by yourself - your lawyer should be doing this, it will carry much more weight. You also need to get an adjournment to the disciplinary in order to allow you to prepare - whether you argue this on the basis of unfairness or illness is really a matter for your legal advisor, but it needs to be done.
I also come from a background in misconduct matters, albeit in a specialist field.
Thinking of you.