Morning MrsJones
There are a couple of ways this can be resolved.
One way is to purchase an Axxess prepaid voucher at either Engen or Pick 'n Pay - vouchers are in the denomination of 1Gb, 2Gb and 3Gb.
On the voucher there will be an username and password, which you can enter on your router's dialling page - this will enable you to have Internet access even though the one account is capped.
Or, alternatively, you can cancel your telkom adsl account (NOT the line, the adsl account only), sign up for an AfriHost 5Gb account which is far cheaper than a Telkom 3Gb account and use that as your primary account.
Do let know if you want more information.
Kind regards
Libs