I forgot where I saw the tutorial, but I remember there was such a method, so I tried it and it worked.
When I was working in Beijing, I applied for a China Telecom broadband: 59 yuan per month, 300M bandwidth. Later, my hometown house also needed a broadband line, so I ordered a cross-province broadband from the Telecom app, same 300M, an extra 40 yuan per month.
Before leaving Beijing for my hometown, I canceled my Beijing Telecom number and bound the Hebei Telecom broadband to one of my China Mobile numbers that I kept for minimal use. Now I only need to pay 40 yuan per month to use it permanently. The only downside is that it will be suspended as soon as there is any arrears. There are no bundled plans and no other charges. If you need it, you can give it a try.