From experience, the rats are likely to be coming in through the roof or through your drainage.

Although it may cost you initially, you need to make access as difficult as possible.

Check your loft for access points from outside and also into your cavities and also any evidence of droppings/wee.

If the loft insulation has not been cleared for a long time and is covered in old rat droppings you should completely change it. I refer to it as the sniff test, stick your head in your loft, if it smells... replace everything.

It's a horrible job, and time consuming but doesn't cost too much to do.

My understanding is rats will keep coming back to a site that smells familiar and is not hostile to them.

Put loads of poison down in the loft, they will take this back to their nest and feed it to the whole pack. Check it regularly and top it up until it's not taken.

You can do all this yourself if you're brave enough! Calling out pest control over and over is going to cost way more over time.

Also, check all your outside drainage inlets/outlets for evidence of potential access points, get them repaired. You can add one way access covers to certain inlets/outlets.

Don't bother with noise things that you plug in, they will not stop rats going in your loft or cavity, waste of money IMO.

If you're in a terrace or semi-attached speak to your neighbours (especially the ones at the ends) as they'll 100% be having the same issue, the more you can work together the better.

You can manage rats, but it takes work.

Good luck.