Collecting usage counters without quota can occur when the original quota is exhausted and reported by the BNG, but the new quota is not given by Policy and Rule Charging Function (PCRF) while UM is still active (not explicitly disabled).
In this case, BNG continues counting. When the new quota is submitted, all consumed bytes up to this point are counted toward the new quota. For example, if 200 units are consumed since the last report, and then a new quota of 1000 units is issued, the 200 already consumed units are counted toward the new quota. For this reason, operators must avoid enabling UM without the quota. This can be achieved by:
disabling UM if it is not needed
submit a new quota by PCRF on every quota report exhaustion generated by the BNG