We are holding RT ticket from BCN to LAX via FRA and plan to use one-way because we are not sure the return date. The ticket is only good for 30 days. Is there any problem if we do not use the return flight coupons? Do we need to call to cancel the return flight? Would LH charge my credit card for full 1-way fare if we fail to use the return?

The fare is non-refundable and non-changeable type of discount fare.