New client VAT authorisation

I have sent the authorisation link to them, but they told me the previous agent holding their gateway account and don't give them any login details. Our client based oversea and they are unable to contact HMRC by phone, is there any options that we can do the VAT return for them? Thank you

Hi James,
Unfortunately, unless you are authorised to act on their behlaf as their agent there is nothing you can do for them. The fastest solution would be for you to get the client to call the VAT Helpline but if this is not possible then you could submit a paper 64-8 - Authorise a tax agent (64-8).
Thank you.