You are with several groups, maybe there are some selected one with huge followers. You also have several telegram accounts because obviously your accounts get banned too. When you get any order you start posting the links maybe with a good message with the hope that the group members will join your client's group. It's like those email blasts in email swap services. Right?
I don't have several groups for this marketing. I don't do that way. I join your group with my accounts, and I invite your competitor's members to your group. Some of them may leave, but if you choose the right audience, drop rate will be very little.