BP Visco 5000 care of Castrol

I am trying to buy more BP Visco 5000 oil. Contacted BP, they were helpful but said I have to phone Castrol for BP Visco 5000 oil, and gave me the number.

I am now a Mozart expert. I have listened to their please-hold tune for 42minutes at a time until I am cut off. The "press 1 to leave a message" does not work either (results in engaged tone).

There has to be an easier way to buy some more oil. It is just impossible to get hold of them by phone.