Until you establish yourself as a reliable seller you will be restricted like this on new selling accounts.

You can attach a credit card to your ebay account. This normally gives you an automatic instant increase to 100.

After that you need to call them monthly (every 30-days) and plead your case for an increase.

We all had to start out this way. Unless you have had the selling account from 10-years ago when these restrictions did not exist.

We have just had one of our selling accounts that started out the same way lifted to 500,000 items per month without even having to ask them. For us that is essentially unlimited. It just takes some time. Took us 3-years to reach this level.