MBD / Discovery collections harrassment!!!!!

I have had enough with MBD Attorneys collecting debt for Discovery Bank, They harass you several times a day. In late January they called me and offered 40% discount on my account. I asked to please send me the settlement letter. Two weeks later I get another call from them (needless to say no settlement letter), offering me the same 40% discount. I once again ask them to send me settlement letter. On 16ht Feb I get SMS;s and e-mail reminders about payment. No instructions on how to pay. I had to contact discovery to get these details. I paid the agreed amount on 23rd Feb and now they are saying I am in breach of our agreement I am liable for the full amount. At no point to do I recall agreeing to a specific date to settle this amount by. THey continue to call me and demand money, each time I ask for feedback on the 40% discount. Even Discovery Accounts does not know about the settlement offer. Absolutely discussting service delivery.