You cannot aggregate links in the way you attempt to do.
First of all:
- 802.3ab is Gigabit Ethernet. It's not a aggregation protocol.
- 802.3i is 10Mb Ethernet.
- 802.3u is 100Mb Ethernet.
- 802.3x is Full Duplex 100Mb Ethernet
- 802.3p is not a recognized standard.
None of the stuff you mention your switch supports is even remotely relevant for aggregation. Especially not aggregation at L3.
Your switch is a standard stupid L2 switch. It has zero management features as far as I can tell, and can simply not aggregate bandwidth from two different L3 devices. When you connect both to your switch, it's basically a round robin selection, where your computer will use either randomly depending on which router was the quickest to answer to your DHCP request. The other will be completely idle.
You need a layer three device to aggregate L3 traffic. That is a router.
There's generally different ways of doing this:
A SD-WAN configuration where you have some remote end that merge the two flows, so it will look like one pipe to the outside world.
Round robin, where network stream A will be sent to modem #1, and network stream B to modem #2, and so forth.
Different clients go to different devices, e.g. computer A -> Modem #1.
In addition the setup is complicated by the fact that it's LTE. The waves is a shared medium, so it's not a given that it's more efficient (or higher performance) with two radios competing for airtime. A single, faster, radio may be a better solution, as it won't have to coordinate with other radios to the same extent.
In short: to aggregate you need different equipment, and if you want one network stream to be split across multiple WAN gateways, you need a computer with fast connectivity somewhere on the internet that can merge those two streams for you.
Switches that support aggregation do so between two Ethernet switches that support aggregation. They will not provide any aggregation over a L3 connection, as LACP is not made for that purpose.
