Poor courier and no response to emails

I run a business and have major difficulties in getting them to collect when customers order from our online store. They are partnered with Courier IT who does the actual collections and deliveries and sometimes they don't collect for several days making customers wait even longer for their orders to be delivered to the pargo points, I even phone them to remind them after they have not collected for a day. I email *** and they never respond so it looks like the only alternative is to stop using them and use PUDO or PAXI instead.