Spam Calls and harassment

ADT handed me over to LGR attorneys without me being in arrears. I was up to date on payments. What happened was that I requested the amount that it would cost to cancel the contract early. I never told them that I was cancelling the contract. And this was confirmed as my monthly instalments were debited as normal. Until I received an SMS saying that ADT handed me over to LGR attorneys (for the amount that I requested!). I did not owe ADT a sent. I paid the amount over to LGR and informed ADT to immediately cancel my contract. Now, LGR is harassing me for proof of payment. It was sent to them last year Nov and I sent it again, but I keep receiving spam calls from their call centre. Pathetic.