Vat advice

We want an opinion on letter-headed paper for treatment of VAT in the following circumstances.

1) We previously over-billed or wrongly billed a customer. We paid VAT to HMRC on the over-billing. In the current period we raised a credit note. We intend to do a credit adjustment to our current VAT return. Is this a correct treatment ?

2) We charged VAT to a USA customer for consultancy services. The work was carried out in UK. We initially charged VAT and paid VAT to HMRC in a prior period. We raised a credit note for the entire invoice and raised a fresh invoice without VAT. We intend to do a credit adjustment to our current VAT return. Is this a correct treatment ?

We want the letter from a tax expert. I am ACCA qualified however not a tax expert hence cannot write a letter to my company. HMRC requires us to have this in writing from a tax expert. The report should be addressed to our company and be dated 30 September 2012 or undated

Please only bid if are a tax advisor in UK