We have done this but the phones still say 'no signal'

Pyramid base

We replaced our old B & O phone with a 2nd hand BeoCom 600 with 3 handsets. As we couldn't delete the previous owners phone numbers, nor rename each phone appropriately, we followed the reset instructions (dot - 7 - 000-8(for base) . After which all 3 phones now say 'no signal'. Thus we can not begin the registration process to link