The only reason that a bank will continually ring is because the client is on an at risk list, I imagine due to previous payment issues. I somehow doubt that they're getting all these calls due to one missed payment, has there been a history of irregular payment problems?
Your 'friend' needs to have a conversation with this bank to come to a satisfactory arrangement that will then take them off this register, which will probably mean arranging a regular payment and discuss any outstanding debts which have yet to be resolved - if there are any due to payment problems historically.
Very few people operate a mortgage in the way you have described. I'm surprised the bank are allowing it to be honest.
Wedding and Party DJ. Resident DJ at the Coach and Horses, Chapeltown. Public Liability Insurance £10M.