In the thread title you have put "Waitrose offer". I presume that it would be more expensive to purchase tickets from the internet.

A search of the internet of the 0870 number you give suggests it's just for the Woman in White performance.

The website for the musical is www.womaninwhitethemusical.com. The site takes ages to go through the introduction, so you might want to go straight to the pages on the performance here.

The 0870 you quote is listed on the tickets page where it says it's 'See'. There is also a Ticketmaster 0870 number.

A search of the Say no to 0870 database shows See Tickets operate a whole host of 0870s. Do a search for SeeTickets (note no space).

The most likely one is labelled "Theatre bookings etc" and it is 0207 4945372. Try that and see how you get on.