Context is everything.
W.r.t. technical issues, focus the conversation on the facts as observed, without getting into too much of a justification or history of why they might not allow the switch.
I.e.,
- Observed fact: It is working on one connected device (the 8800L and the prev. 7730L)
- Observed fact: The new equipment has been certified for use on the Verizon network (but you may want to hold off on that statement until it actually is certified (if it is a CAT18, see Verizon Certification - #9 by Helen_Aziz)).
- Observed fact: The speed seems to be throttled or deprioritized (i.e., slow) whereas on the previous device it was not.
- The IMEI of the unit.
They have all the plan information about you, and if, in the end, they claim that your plan does not allow the device then it is time to request the contract terms that prohibits its use (or accept it an go on with life).
On the other hand, it might simply be that the move of the SIM card to the new device triggered a check, and they discovered that you had moved the SIM card from a phone/tablet (in the original plan) to a “connected device”
Since carriers now have started caring about IMEI numbers on plans, I expect the only remedy is to get tech. support to agree that the line needs to be categorized as a “connected device,” and make the manual change required (we had that happen to one of the lines, originally a SIM on an iPad that moved to a CAT4 BR1 (successfully) and then to a CAT 6 BR1 (requiring tech. support intervention)).
Preparatory to all this you may want to log into the Verizon site and check what equipment they believe the line is connected to. E.g., in our experience, the line in question was showing as an iPad when it was installed on a BR1 CAT4 (and working well) and trouble started once we moved it to the BR1 CAT6. (Curiously, they still list the line’s device as the old iPad…)
Good luck.
Z