An antenna that supports the Telstra 4G network is what they must be suggesting as it is a Telstra service. ALDIMOBILE are using the Telstra Wholesale network. Repeaters for the Telstra network are around $1,000, if they are instead suggesting a repeater.
An antenna will require a connection to your mobile device or to your router if the router is using the mobile network. A repeater may also use an antenna to increase signal strength gain, a repeater does not need to be attached to the phone that is benefiting from the signal boost.
If the Telstra Internet is by copper connection, this is owned by NBN Co not Telstra.
If you wish to complain about your mobile reception, you should first complain to your provider, in your case ALDImobile. Telstra are not your provider and you are not their customer, they supply a service to ALDImobile who then supply a service to you. That Telstra replied to you at least indicates they have some level of interest in you getting some improvement, even if the answer you received was quite simple and perhapsââcurtâ.
Under the Mobile Blackspot program, Telstra, Optus, and Vodafone/TPG can apply for Federal funding to increase their network in areas where reception is poor or nonexistent. Complaining to your provider who is a MVNO (so not an owner of any network) and asking them to look into submitting a request to their provider for improvement using the Blackspot program would be a good step in trying to get the longer term problems addressed. Also contacting you local Federal House of Representatives member and your State/Territory Senators is another good step. Have your neighbours also make the same approaches, the more contacts made means that the major Telcos get more feedback to encourage them to apply for funding in your area.
Shorter term, a Booster plus an antenna, should improve your âin homeâ coverage. Buildings, landscape, and foliage block signals, unimpeded line of sight to a tower will give the best reception, any impediments will decrease or obliterate signals and so either poorer or no reception is possible.
Telstra provide a unit that may help but it will cost you and needs an assessment by Telstra (also probably at a cost to you).
Examples of 4G antennas (not a recommendation of the businesses or the products, just for information).
https://rfshop.com.au/product-category/antennas/4g-5g-ready/
All of these need a device that is able to connect to the antenna, most mobile phones these days do not have connectors for external antennas. Often then what it needs is a booster/repeater that connects to that external or in the home antenna (best antenna is external). The only approved option in Australia is a CEL-FI product, Telstra rebadge them when they supply them but you can buy the products without using Telstra, Optus, or Vodafone/TPG but they do need to be approved/licensed for the network you are using them on.
Some examples of packages (not a recommendation of the business, provided purely as examples for selection and cost).
The cost even if purchased via Telstra is expensive.