Good Evening,

it generally helps to provide more information, such as a website address, or postal address.  Thankfully I know the ASDA site quite well.

This page which is accessed via the main ASDA site gives 2 numbers to call, the one you have given has an address of:
ASDA Car Insurance
MMT Centre
Severn Bridge
Aust
Bristol
BS35 4BL

Typing MMT Centre into a search engine, gives us the Brightside Group.

So it would appear that your ASDA policy is administered by a subsidiary of Brightside Group.

If you type Brightside into the search page on the main SayNoTo0870 site there are a few numbers to try.

Please let us know if any of them are suitable.