Incorrect VAT data - messed up transactions - Start fresh?

I have had quite a disaster with Quickbooks online with regards to the VAT reports. Quickbooks is taking the invoiced figures as an income, also deposits for the same invoices, therefore doubling income, and also listing what should be expenses as incomes, even though all those expenses are listed as 'expenses', Therefore the VAT due on sales is completely wrong, as is the VAT to be reclaimed on purchases.

Not only that, I hired a bookkeeper to help get things in order, and all she did was void off loads of invoices which again, make the whole VAT  figures incorrect.

Should I just wipe the whole system clean and start fresh? Then Quickbooks can download all the information directly from the bank account, as surely that is a definite correct base to work from? How far back will Quickbooks draw information from the bank?