Unfair business practice

I had made an arrangement for intellicell to collect the money from my account after skipping a payment in May, they only debited the current month's installment and now they've blocked my phone while it's them who didn't collect the amount we agreed on. This is an unfair business practice and now the lady who they're saying is handling my account is becoming rude and very difficult while she is the one I had made an arrangement with.