Well that's wrong. 50P a month of the referral value is from phone line so based on the fact you have 2 referrals yours would drop from £2.50 to £1.50 as you would have 2 x 75p which is the fibre referral.
No, u wrong there. If the referral from other person move away or left plusnet I will lose it. The referral is nothing to do with my active phone line or fibre. It was other round it.
Perhaps if any of your referrals have their line rental with PN you could persuade them to move their line rental to the PO as well, then you could lose those referrals and pay even more!
My original facetious suggestion was as quoted immediately above, and pcoventry76 was quite right in his/her explanation if you had followed that course of action.
Which doesn't detract from the original point of fact that you would have been paying £2.50 more per month for your Internet Service from PN had you moved your line rental to the PO.