It's worth trying for a discount, but bear in mind the following:
1) VM don't want to make discounts too readily available, it's not just a case of asking, and you may find it a n endurance trial to get through on the phone to the retentions team. The Whatsapp method can work, but as it isn't real time may take a while.
2) Full price is very high, few people are paying it - VM's average revenue per broadband customer was less than £49 a month in most recent investor communications, showing that the majority of customers fit into two categories: on slower speeds and minimal content bundles, and/or they have a sizeable discount.
3) As and when you get through to Retentions, asking for a discount alone doesn't get you far. Neither loyalty or fairness count for anything, the only thing that counts is whether the agent really thinks a customer will leave. Know what you'd pay for an equivalent service from other suppliers (including their new customer discounts) and quote that to the agent. Whether via voice call or Whatsapp, your opening gambit needs to be something around "thinking of leaving due to cost of living, need to cut back, seen great offers from (eg) Sky or BT, so wondering about cancelling...."
4) If you get a reasonable offer over the phone, you have to take it then and there - regardless of what the agent may say, phone discount quotes are only valid during the call concerned, and they don't stay on the table for you to consider. With the Whatsapp method, because it isn't real time you do get more time to think before accepting. Screenshot any offered and accepted deal details.