Failure to cancel and still debited

I am disgusted at Rain and how careless they are. My mom cancelled her subscription with effect from 1 June. They advised the last debit will be on the 1 June which was fine. They ended up not cancelling her subscription and debiting her on the 1 July again. She requested a refund and till date they have still not returned her money after they collected their device and all. Each time she speaks to them there is a new excuse yet they are at fault here and she is a pensioner.